Naval AntiAircraft Guns and Gunnery

By Norman Friedman

This book does for naval anti-aircraft defense what Friedman’s Naval Firepower did for surface gunnery – it makes a highly complex but historically crucial subject accessible to the layman. It traces the growing aerial threat from its inception in WWI and the response of each of the major navies down to the end of WWII, highlighting in particular the underestimated danger from dive-bombing. The work considers what effective AA fire-control required, and how well each navy’s systems actually worked, analyzing the weapons, how they were placed on ships, and how this reflected the tactical concepts of naval AA defense. All important guns, directors and electronics are represented in close-up photos and drawings, and lengthy appendices detail their technical data. It is, simply, another superb contribution to naval technical history by its leading exponent.

• Language: English
• Publisher: Naval Institute Press
• Release date: Feb 15, 2014
• ISBN: 9781612519579

Norman Friedman

NORMAN FRIEDMAN is arguably America’s most prominent naval analyst, and the author of more than thirty books covering a range of naval subjects, including Naval Anti-Aircraft Guns & Gunnery and Naval Weapons of World War One.

Book preview

INTRODUCTION

One of the more enduring images of Second World War naval warfare is of a ship defending herself against hordes of air attackers. The US Navy, the Royal Navy and the Imperial Japanese Navy found themselves under particularly heavy air attack. This book is the story of how that defence was developed and of how well it worked for the different major navies. Post-war developments indicate the conclusions the major navies drew.

This story would make no sense without taking into account the impact of the Great Depression. For the United States, the Depression began in 1929, and it did not really end until the country mobilised for the Second World War beginning in 1940. Attempts at recovery beginning in 1933 included some new construction, but always under tight economic conditions which limited what else could be bought. That is a major reason why the US Navy was so very under-armed in light anti-aircraft weapons in 1940. The country was fortunate that it could mobilise, even if incompletely, before it had to fight. More money was available before the 1929 Crash, but successive administrations considered military and naval spending a drag on the economy. In retrospect that was no very bad thing, because heavy spending in the 1920s would have produced large quantities of obsolete equipment. Aircraft were changing far too rapidly, particularly in the 1930s.

Rapid pre-war expansion brought its own problems. The navy found itself flooded with new personnel, who had not received extensive training in technical schools before encountering such increasingly sophisticated equipment as the Mk 37 fire-control system. Exercise scores fell, even though targets did not change very much between 1939 and 1941. Again, fortunately for the United States, much of the necessary training was completed by the time war broke out – when even more new sailors arrived.

The situation in the United Kingdom was more complicated. Before the First World War the Royal Navy was clearly the most advanced in the world, and during the war it gained far more experience than its rivals. Despite the crippling cost of the war, it was able to continue development after the war. It also had an enormous overhang of existing modern ships, so new construction was not too urgent during the 1920s. Beginning in 1919, the British adopted the ‘Ten Year Rule’ for planning, the assumption that they would not face a major war for a decade. By 1929 it had been made self-perpetuating. Initially the rule was probably mainly a way of emphasising the need to modernise in view of changed orientation (towards a Japanese threat), but ultimately it became a way to cut expenditures so as to promote economic recovery from the remaining damage done by the First World War. Ultimately the effect of the Rule was to cut expenditures on expendables, such as shells and fuses. Thus, when the situation was reversed and the initial recovery programme concentrated not on ships or guns but mainly on items such as shells and fuel reserves and quartz for sonar transducers.

As in the United States, the effect of the Depression was to limit new production, although work on prototypes continued. Unfortunately the British felt constrained to mobilise much earlier, because the Japanese advance in the Far East threatened them more directly. The ‘Ten Year Rule’ was dropped in 1932, and by 1934 a Cabinet committee originally formed to develop disarmament policy had been transformed into the Defence Requirements Committee (DRC), responsible for making up deficiencies accumulated under the ‘Ten Year Rule’. At about the same time, before Hitler rose to power in Germany, some in Britain saw Europe skidding towards war. That was another reason to repair deficiencies in defence, but it also greatly complicated the British position – the country faced war both in the Far East (which the Royal Navy had long envisaged) and in Europe. The Royal Navy formulated its anti-aircraft rearmament programme in 1936, after the shock of nearly having to go to war with Italy over the Abyssinian (Ethiopian) Crisis.

From an air defence perspective, mobilisation (or rectification of deficiencies, as it was initially) meant that the Royal Navy had to continue to produce existing weapons and fire-control systems, whatever their deficiencies: the iron law of mobilisation is that you produce what is on hand – you do not wait for something better. The Depression compounded the problem by dramatically shrinking the British industrial base. As the country recovered in the mid-1930s, its industrial pattern changed away from what the Admiralty had previously relied upon, so it became more difficult to build back-up. Developing entirely new systems while mass-producing existing ones was less and less possible. That is why the Royal Navy entered the Second World War with totally inadequate high-angle control systems. It had no real alternative. The navy and its ordnance organisation knew what was happening, but that did not really matter.

The Royal Navy’s view of ship design requirements also had a considerable impact. Given the worldwide empire, the Royal Navy always had to take the need for numbers into account. The Admiralty generally equated ship size with cost. Cruisers were a particular problem. In the 1920s the Admiralty estimated that it needed seventy cruisers. It found the new 10,000-ton ‘Treaty Cruisers’ ruinously expensive, and British delegates to the London Naval Conferences of 1929 and 1935 sought to curb the size of foreign cruisers so as to make the desired number of British cruisers affordable. The 1930 London Naval Treaty prohibited further construction of cruisers armed with 8in guns, but at a high price: the Royal Navy had to agree to near-parity with the United States, which did not have a global empire and needed many fewer ships. The British believed that rational foreign navies would be satisfied with cruisers about the size of its Leanders, about 7000 or 8000 tons rather than 10,000 tons. They were shocked when the US and Imperial Japanese Navies both laid down much larger ships. The British felt compelled to build their own large cruisers, the ‘Town’ class – which they could hardly afford in sufficient numbers. They finally solved the problem in the 1936 London Naval Treaty, which limited future cruisers to 8000 tons. Only the British actually built ships of this size, the Fiji class. The US Navy designed an 8000-ton cruiser (CL 55), which led it to design a dual-purpose 6in gun as armament, but once war broke out in 1939 the treaty was considered defunct, and the CL 55 actually ordered was the 10,000-ton Cleveland.

Anti-aircraft guns in...

Anti-aircraft guns in action: 4in Mk V HA guns on board the Australian cruiser Sydney. (State Library of Victoria)

All of this had painful implications for the Royal Navy. The Fiji design packed the armament of a 9100-ton ‘Town’ into an 8000-ton hull. The ‘Town’ had a heavy anti-aircraft battery by pre-war standards, but early war experience showed that those standards were grossly inadequate. Unfortunately the ‘Towns’ and other British warships turned out to be too tightly designed to accept much additional light anti-aircraft armament without considerable sacrifices. The British experience contrasts with that of the US Navy, which managed massive increases in light anti-aircraft weapons as the war progressed. It is possible, too, that British standards of stability prohibited anything on the US scale; the Royal Navy often operated in rougher waters.

Money was too short...

Money was too short between the wars to replace the obsolete Mk 19. The best that could be done was to combine it and a new stereo rangefinder on a single enclosed mounting, which was called Director Mount Mk I. It was installed during 1939–40 on board US battleships and cruisers. The boxy director mountings are evident fore and aft on board Northampton, photographed in Brisbane between 5 and 10 August 1941. The opportunity was taken not only to integrate rangefinders and directors, but also to move the directors to the centreline, where they had much better arcs (later cruisers had directors on the centreline). Modernisation included doubling the medium-calibre anti-aircraft battery to eight single guns, the number in later cruisers. As early as 1937, the US Navy planned to modernise its newest battleships (the ‘Big Five’) with newer Mk 33 directors, which were considerably better than Director Mount Mk I, but that was not done. (USN courtesy of Edward L O’Neill, 1983)

The medium-calibre long...

The medium-calibre long-range anti-aircraft fire-control systems used in the Second World War can all be traced back to those of the inter-war years. Because very little money was available in the 1930s, the key issue was whether earlier, unsatisfactory, systems could be the basis for step-by-step development into something effective. At first glance the US Navy’s Mk 19 director (centre) flanked by two separate ‘altiscopes’ on board the heavy cruiser Chicago looks distinctly unpromising. Operators at the director looked at the target and corrected aim, but because the altiscopes (range- and heightfinders) were physically separate the director operators could never be sure that they and the altiscope operators were even tracking the same target. The connection to fuse-setters at the guns was even more tenuous. However, the tachymetric concept embodied in the director was viable. The next step was to adopt stereo rangefinders which could be installed in an integrated director, effectively combining the altiscope and an evolved Mk 19 as Mk 28 and Mk 33, the main prewar medium-calibre systems. The step beyond, which created the successful wartime Mk 37, was to clear the director by moving the computer below decks, connecting it with the director by synchros and power drives. At the same time the fire-control system was more tightly integrated with the fuse-setter, which ultimately was placed in the ammunition hoist. This photograph was taken at Mare Island in 1931. The hooded object below the anti-aircraft fire control platform was a main-battery director.

The inside of a...

The inside of a Director Mount Mk I shows just how simple it was; the object in the foreground is largely unmodified Mk 19 director. This illustration is from the manual, issued in July 1940.

In both the United States and the United Kingdom, the impact of the Depression was to reduce training and to defer desired anti-aircraft upgrades (such as additional guns) and, more subtly but probably more importantly, to defer purchases of expendables, such as ammunition and, crucially for anti-aircraft warfare, fuses. Training time mattered enormously, not only because it determined how well systems would perform in wartime, but also because training exercises were generally the source of the navies’ expectations as to wartime system performance. They shaped what the navies thought they needed. Only at the end of the Second World War did the US Navy form a special dedicated experimental test and evaluation unit. Until then experiments and training were tied together.

For the Royal Navy, the Depression deferred the introduction of radio-controlled drone targets, which would have done a lot to make target shoots more realistic and thus might have goaded the Royal Navy towards developing more effective forms of fire control in time for the Second World War (it is not clear that the US Navy had the potential to adopt target drones much earlier than it did). The Royal Navy used its drones differently from the US Navy, and they could not simulate dive bombing. At the end of the war, the commander of the British Pacific Fleet argued that his fleet’s poor anti-aircraft performance, compared to that of the US Navy, could be traced in part to its lack of realistic anti-aircraft training (the US Navy was plentifully supplied with drones). For both navies, despite clear understanding of the consequences, it was impossible to replace powder time fuses with mechanical ones, given the huge numbers involved. The US Navy had to accept a very high rate of duds and low-order detonations, which may not have been obvious until it began using drones for target practice in 1939. As late as 1941 the Bureau of Ordnance had to warn the fleet that the next year it would have to use powder fuses for half its practice firings.¹

The third major naval power, Japan, had yet a different experience. Despite the effect of the Depression, and also despite relative poverty, successive Japanese governments continued to spend heavily on their fleet. They did not spend much on developing entirely new systems, although there were major exceptions such as the ‘Long Lance’ torpedo. In particular Japan could not develop new industries such as electronics to anything like the level of the much wealthier Western powers. In effect Japan mobilised continuously between the World Wars, and it too obeyed the iron law. With important exceptions (mainly naval aviation), the Imperial Japanese Navy of 1941 was a superbly developed First World War navy. Like Britain and the United States, Japan developed radio-controlled target drones.

By 1940, with the...

By 1940, with the world in crisis, the US Navy could deploy the medium-calibre system it would use during the Second World War, albeit as yet without radar. Hillary P Jones is shown on 14 December 1940. British observers were impressed by the all-dual purpose main battery and the Mk 37 fire-control system (as yet they were probably unaware of the integrated fuse-setters in the ammunition hoists). The US system included a stable vertical (a vertical reference used to stabilise the director) and RPC for the 5in guns. The British argued, however, that US destroyers were top-heavy compared to their own ships; the US Navy did not contemplate the sort of rough waters the British expected. Nos 3 and 4 mounts were unshielded in order to save weight. Notably lacking was much of an automatic battery to beat off dive bombers. This ship could accommodate a pair of 0.50-calibre machine guns on the platform below the searchlight aft. In 1940 the US Navy doubted that defence against such attack was really practicable; it expected to rely on barrage fire by medium-calibre guns. By December 1940 the Royal Navy was using such ‘umbrella barrages’ in action.

By 1941 the US...

By 1941 the US Navy wanted splinter protection for all its guns. Gleaves, a sister-ship of Hillary P Jones, is shown after a Boston Navy Yard refit, 18 June 1941. Nos 3 and 4 guns are now half-shielded (they have no roofs); full gunhouses would have added too much weight. Note also the gun tubs, for 0.50-calibre machine guns, around her after stack. She had another pair of gun tubs just forward of her bridge structure on her 01 level. Her after bank of torpedo tubes had been removed as weight compensation. The next step was to replace No 3 5in gun with a pair of twin Bofors, from 1942 onwards.

More generally, aircraft were the exception to the slow development of fleets between the wars. In the 1920s and 1930s they were inexpensive, and the potential for development was huge. Particularly in the United States and in Japan, relatively small investments in naval aircraft development had huge payoffs. From the point of view of naval air defence, that meant huge changes in requirements and the obsolescence of earlier systems. Thus the Royal Navy, which had been quite air-minded and had deployed an advanced high-angle fire-control system in the 1920s, found it difficult to devise an entirely new system capable of keeping up with a rapidly-evolving threat in the 1930s. On the other hand, because the United Kingdom developed a large electronics industry between the wars, it was able to deploy radar in quantity and with high quality. Radar in turn made it possible for the Royal Navy to make up for deficiencies in anti-aircraft gunnery by controlling fighters against enemy bombers. The Imperial Japanese Navy had no such potential, because it had spent most of its money on pre-electronic forms of naval warfare.

The limited cost and rapid development potential of aircraft explain why Germany, which created a large military machine so rapidly, emphasised them both ashore and over the sea. For the Germans aircraft were also attractive because most people saw them as the embodiment of the future. Hitler and his Nazis represented themselves as the future of Germany, and it was natural for them to make the Luftwaffe integral with the Party. To some extent Mussolini had a similar view of aircraft and his air force, although the result was less successful than Hitler’s. German and Italian shore-based aircraft were the key elements of the war the Royal Navy fought in the Mediterranean.

During the Second World War it was not well understood that although aircraft might be plentiful, experienced aircrew were not. Only after the war did it become clear how devastating losses could be, particularly if new aircrew were not being trained rapidly enough. Thus after the successful ‘Turkey Shoot’ which wiped out the Japanese carrier air arm during the battle of the Philippine Sea (June 1944), US naval aircrew were depressed because they had not dealt with most of the Japanese carriers – a view which carried over into the success of the Japanese decoy force (consisting of carriers with few aircraft) at Leyte Gulf (October 1944). The Japanese were particularly affected because they had decided against expanding their aircrew training programme. Although most aircraft were shot down by fighters, guns did their share. In the Japanese case, the loss of aircrew led indirectly to Kamikaze tactics. After the bloodbath in the Solomons in 1942–3, few of the highly-trained pre-war aircrew remained. Their relatively untrained successors performed much more poorly, particularly since they faced more and more formidable defences: better US fighters flown by increasingly experienced pilots and directed by radar, plus much more powerful anti-aircraft batteries with better fire control and proximity fuses. When asked after the war to justify Kamikaze tactics, a senior Japanese officer remarked that few aircraft returned no matter what the tactics; better to adopt tactics which promised to achieve something for the inevitable sacrifice. That was apart from the possibility of greatly multiplying the number of attackers by using all available pilots, including partly-trained ones. Those pilots could not have executed conventional attacks.

Details mattered enormously. Most anti-aircraft guns, down to about 40mm or 37mm, were power-worked. If a ship lost power, they were nearly useless, even if they had alternative manual controls (which could not move them nearly fast enough to track targets). After HMS Prince of Wales lost power due to a very unlucky torpedo hit, her powerful light anti-aircraft battery was suddenly reduced to a single Bofors on her quarterdeck and a few Oerlikons. No wonder her gunnery officer thought that Bofors was worth all her pom-poms; but he did not realise that the only way to wield massive anti-aircraft firepower was to accept power operation. The flaw in the ship’s anti-aircraft armament turned out to be the absence of emergency diesel generators, of the type the US Navy and not the Royal Navy provided.

Similarly, the way in which fire controls and associated equipment was connected to guns mattered. Until the 1930s the Royal Navy relied entirely on step-by-step motors to transmit data, for example from a fire-control computer to a gun mount. These devices are simple and robust, but their action is abrupt, as they click from one setting to the next. The Royal Navy seems to have rejected stabilisation in anti-aircraft systems because that required smooth transmission from a stable element to the guns and directors. By the time the Royal Navy had a smooth enough form of transmission (Magslip), it was too late to reverse the earlier decision, because Britain was mobilising.

Pre-war financial restrictions...

Pre-war financial restrictions precluded development of a fire-control system for the 3in/50 gun, which armed the ten Omaha class cruisers and the oldest battleships, among others. At best, these ships could only fire barrages through which, it might be hoped, an attacking aircraft might fly. As war came closer, old destroyers like Overton, shown, were rearmed with six 3in/50s – but they too had no special fire-control systems, and to describe them as anti-aircraft escorts was unfortunate at best. As late as 1943 destroyer escorts armed with 3in guns lacked any fire controls.

Much the same might be said of the British decision not to adopt stereo rangefinders for anti-aircraft fire. Coincidence rangefinders, particularly the horizontal ones used by the Royal Navy, proved ill-adapted to anti-aircraft operation. Rangefinding problems helped convince the British to accept what turned out to be a poor high-angle control system, in which target speed had to be estimated on the basis of perceived target type. Only in 1943, with the evidence of US stereo rangefinding before it, did the Admiralty admit that it should have adopted stereo techniques for air defence.

Technical details have been presented to give a clear idea of what the major navies were doing during the supposedly empty inter-war period to protect themselves against air attack. Although their efforts were not entirely effective, it is clear that they were extensive. Details also make it possible to compare different approaches, particularly those of the Royal Navy and the US Navy, in as objective a way as possible. To the greatest possible extent, this material has been taken from contemporary internal documents rather than from later ones.

For continuity, the story of systems conceived before the war has generally been continued into the Second World War in the inter-war chapters, the wartime chapters concentrating on entirely new wartime developments. Thus in the US case the various Bureau of Ordnance machine gun directors (Mks 44, 45, 49) conceived in 1940 are in the pre-war chapter, but the wartime Mk 51 and its ilk are in the wartime chapter. Similar logic applies to the other navies. Except for the US Navy and the Royal Navy, virtually all wartime equipment was of prewar conception and design.

Sources

This account concentrates on the US Navy and the Royal Navy because they were by far the most advanced exponents of anti-aircraft gunnery between the wars and during the Second World War, and because their post-war work on guns and fire control reflected their extensive wartime experience. Their story can be told almost entirely on the basis of primary documents. The quality and quantity of documentation differs considerably. Much of the US naval ordnance material, including correspondence files and weapon and fire-control handbooks, has survived, though much less has survived of publications explaining how weapons were to be used. Far less of the corresponding Royal Navy material seems to exist, but the annual official publication Progress in Naval Gunnery tells much of the story. Many British handbooks, some with no surviving US equivalents, have also survived. The rough US equivalents to Progress in Naval Gunnery are the more or less annual Bureau of Ordnance Confidential Bulletin and the voluminous annual Reports on Gunnery Exercises. For ships the most important surviving British documents are the Ships’ Covers and constructors’ notebooks. The reader should be aware that constructors showed little interest in weapon development, though Covers do occasionally include relevant material, and they also often reflect shifts in anti-aircraft thinking.

Other major navies seem much less completely documented. French archival documentation has been supplemented by some publications. The French made extensive pre-war efforts to develop anti-aircraft firepower even though they did not have much opportunity to use their systems during the Second World War. To some extent pre-war work was the basis for post-war development. Documents collected or produced by the victorious Western powers after the Second World War provide insight into developments in Germany, Italy and Japan, but information is limited. The account of Soviet developments is based on published Russian-language material, which has, fortunately, become available in quantity with the end of the Cold War.

By the end of...

By the end of the Second World War, the fusion of surface anti-aircraft fire and fighter defence was symbolised by radar picket destroyers like Chevalier, shown off Hampton Roads, newly converted, on 24 May 1945. A tripod radar mast replaced her forward bank of torpedo tubes; the after bank was replaced by additional anti-aircraft guns. The mast carried, top to bottom, a YE aircraft homing beacon, an SP pencil-beam aircraft-tracking and heightfinding radar, an array of enemy radar receiving antennas (on the yardarm), and a TDY jammer (on the lower platform). The fleet had discovered the value of radar picket destroyers stationed well forward of a force in the direction of a likely threat, and at Okinawa it set up fifteen radar picket (RP) stations, each of which was manned by a destroyer and supporting craft, particularly fire support landing craft (LCS). Ships in the anti-submarine and anti-surface screens were also used as radar pickets as the situation demanded. Each picket was to open fire on any unidentified aircraft which came within 12,000 yds. The destroyers were not specially fitted, but they did have fighter controllers on board. They were primarily radar guards to provide the fleet with early warning. Although not primarily fighter directors, they could be assigned to that role. Pickets were placed 75 miles from the centre of the defended area. That made it possible for them to pass control of friendly fighters from one to another, but not close enough for mutual support when attacked. The SP radar on board a specially-converted radar picket fed a more sophisticated combat information centre on board the destroyer. Destroyer radar picket losses off Okinawa were so severe that alternatives were sought for the planned invasion of Japan: either smaller and hence less valuable pickets (converted destroyer escorts) or submarines, which could submerge in the face of the worst threats. Both were in process when the war ended.

CHAPTER 1

AN EVOLVING THREAT

Unlike surface gunnery, anti-aircraft gunnery developed in the context of a rapidly-changing threat. There were also changes in the way in which navies evaluated the air, compared (say) to the surface, threat. There was already an air threat in 1917–18. The Germans and the British both used torpedo bombers in combat, and the British considered reconnaissance Zeppelins a major problem in the North Sea.¹ Aircraft were prominent enough in anti-submarine warfare that some submarines were given heavy anti-aircraft guns. When the Royal Navy reviewed the situation in 1931–3, its Naval Anti-Aircraft Gunnery Committee cited the rise of ship-based aircraft in the US, British and Japanese navies, French flying boat operations over the Mediterranean, and the impressive mass Italian long-range flights (mainly led by Italo Balbo: the formations were often called ‘Balbos’).

Air Arms

The US Navy and the Imperial Japanese Navy both had their own air arms during the inter-war period. The US Navy became particularly air-minded. It created an instant corps of senior naval aviators by requiring all commanders of naval aviation activities and ships (including carriers) to have either ‘wings’ or aviation observer status. Ambitious officers sought the necessary training and gained an aviation perspective. The United States also created a large naval air arm, which it demonstrated to itself in the annual Fleet Problems (fleet exercises) in the Pacific. The Fleet Problems and also nearly compulsory senior officer education at the Naval War College (where the students worked out phases of the war plan against Japan) educated even non-aviators in the impact of naval aviation. For example, after one Fleet Problem in the late 1930s, the main complaint of the battleship officers was that the carriers had fought what seemed to be a private war, denying them the air services, including fighter cover, they wanted. Rear Admiral Ernest J King (Commander, Air Squadrons, Battle Force and later wartime Chief of Naval Operations) pointed out that the carriers could easily destroy each other. If they did not fight their ‘private war’, the battleships would never have any air services, because all the aircraft would be on the bottom. Typically US carriers operated well away from the battle line, which was easily spotted at a distance, in order to make it more difficult for enemy scouts to find them. That contrasted sharply with contemporary British thinking. King’s insight, which probably was widely understood, emphasised the need for anti-aircraft weapons, because at times the fleet would have to defend itself.

In support of the carrier vs. carrier war, in the late 1930s the US Navy decided that its dive bombers would have an alternative role as scouts; they were therefore designated in an SB series, as in the SBD Dauntless. US carriers typically had four squadrons on board: one of fighters, one of dive bombers, one of scouts, and one of torpedo bombers. Until the advent of radar, there was little hope that the fighters could effectively protect the carriers, which operated singly. The fighters were intended more as strike support, helping the strike aircraft deal with any defending fighters and probably also helping by strafing enemy air defence control and guns.

The pre-war Imperial Japanese Navy also had a large carrier force. Unlike the US Navy, the Japanese followed the Royal Navy (see below) in equating carrier aircraft capacity with hangar capacity.² Typically their carriers had three rather than four squadrons on board. That is why the three US carriers at Midway had about as many aircraft as the four Japanese carriers they faced and defeated. On the other hand, in 1940–1 the Japanese succeeded in creating multi-carrier Air Fleets which could fight as single entities. Overall, they had little faith in air defence: the enemy carriers had to be destroyed before they could strike. The Japanese depended mainly on fighters rather than on shipboard anti-aircraft guns for fleet defence. However, they appear not to have appreciated the importance of fighter control, e.g. to keep fighters from being drawn entirely to counter one raid while another might be approaching. For them, Midway was an object lesson in just such failure: the defending fighters were drawn down to deal with the US torpedo bombers leaving the way open for the dive bombers. Without radar and also with poor voice radio, fighter control was impossible.

The Mitsubishi G3M (‘...

The Mitsubishi G3M (‘Nell’) made up the bulk of the Imperial Japanese Navy’s considerable land-based bomber force when the Pacific War began, and this bomber also made up the majority of the force which sank Prince of Wales and Repulse. The object under the belly of this ‘Nell’ is the rack for a torpedo or bombs. (Phil Jarrett)

The most important factor...

The most important factor in air operations against ships is that the sea is so broad. Air attacks cannot be mounted until the enemy is found. That is why signals intelligence was so important in the Second World War: when it worked, it showed the attacker where to search. Operations in narrow waters were of course simpler, but they always required search before attack. The Japanese used shipboard floatplanes to find enemy fleets. In 1942 the Japanese naval staff tried an alternative, the high-performance carrier aircraft shown here. This C6N1 Saiun (‘Myrt’) was designed to a Spring 1942 specification requiring a maximum speed of 350kts and a range of 1500nm at 210kts (maximum 2500nm). The Saiun flew in May 1943 and was accepted even though it did not achieve the desired speed. During the battle of the Philippine Sea, Saiuns effectively shadowed the US fleet, their high speed protecting them from interception. They were responsible for the great success the Japanese enjoyed: they were able to attack from well beyond the attack range of the US fleet. That did them little good, because US fighter control and US anti-aircraft guns were so effective. This ‘Myrt’ was captured on Saipan in June 1944.

The wartime successor to...

The wartime successor to ‘Nell’ was the G4M (‘Betty’), which, like its predecessor, could deliver both bombs and torpedoes. G4Ms were part of the attack against Repulse and Prince of Wales, and later in the war they executed effective night torpedo attacks against US carriers and cruisers. At the end of the war they launched Okha manned stand-off missiles. (Philip Jarrett)

Like their US counterparts, Japanese cruisers carried floatplanes assigned to scouting as well as spotting duties. In the US Navy, the floatplane scouts were intended for use when the cruiser or cruisers operated independently, far from the fleet. Unlike the US Navy, the Japanese used these same floatplanes to scout for carriers screened by the cruisers, as at Midway. Wartime US and British observers considered that the problems of tracking enemy fleet units and of coaching a strike force into position had received particular attention in the Imperial Japanese Navy.³ Scouting was considered so important that, unlike the US Navy, the Japanese separated it from strike, to the extent that scouts were ordered to avoid combat if possible so that they could complete their scouting missions. The fleet scouting mission was symbolised by the design of the Tone class cruisers, with their open aircraft areas aft. Only during the war did the Japanese develop a specialised high-performance carrier scout, the C6N1 Saiun.⁴ It had no Western equivalent. Wartime Japanese air tactics envisaged a scout or snooper working with a strike force, using elaborate tracking and liaison techniques. By 1943–4 Japanese scouting aircraft had radar. They were advised to minimise both radar and radio transmissions until the moment came to home the strike force on the target, at which time there had to be a considerable volume of traffic to and from the tracking aircraft. On this basis communications volume became a reasonable indication that a striking force or a relief shadower was being homed on the target.

Japan was unique in having both a carrier air arm and a substantial naval land-based air arm. The US Navy also had a large shore-based air arm, but it consisted of flying boats, not high-performance bombers like the G3M ‘Nell’ and its successor G4M (‘Betty’). ‘Nell’ was built to a requirement conceived in 1933 by Admiral Yamamoto, who was then chief of the technical division of the Japanese Naval Bureau of Aeronautics (the equivalent of the US Navy’s BuAer). Admiral Yamamoto was aware of developments which gave twin-engine aircraft very high performance (which in Britain was taken to mean that ‘the bomber will always get through’) and he asked for an aircraft capable of maintaining surveillance over Pearl Harbor, the US fleet base, from Japanese airfields. Such surveillance was necessary if, as the Japanese hoped, they could intercept and defeat the US fleet before it reached their home waters. The aircraft also had to be capable of carrying out attacks at long range. Yamamoto and others were interested in using a force of land-based bombers which could shuttle among the Micronesian islands Japan then ruled as League of Nations mandates. It was clear that the flying boats Japan was using at the time lacked the requisite performance.⁵ The requirement was in accord with the Japanese naval strategy of wearing down an approaching US fleet before it encountered the main Japanese fleet, and the high performance envisaged would give the new bomber a reasonable degree of immunity against the fleet’s fighters. Yamamoto chose Mitsubishi as sole-source developer because that company had imported engineers from the German company Junkers (which was building high-performance twin-engine bombers) specifically to obtain the technology involved. In effect ‘Nell’ was the air power equivalent of the Yamato class battleship: a technological solution to the numerical inferiority of the Japanese battle fleet. The ‘Nell’ entered production in June 1936. As the longest-range Japanese bomber, it participated in the war against China that began in 1937, first carrying out attacks from Formosa in August. These operations made the British aware of it, though not of its extraordinary range. It also appears that the British tended to mirror-image, and thus to associate all land-based bombers (such as G3M) with the Japanese army, not the navy. That may have blinded them to the threat of such aircraft (in 1942 US air intelligence was counting Japanese biplane torpedo bombers as the aircraft which sank the two British capital ships).

The Heinkel He 111H...

The Heinkel He 111H-6 was the main German wartime land-based torpedo bomber, typically carrying two torpedoes (in this case practice F-5bs) as shown. Numbers were always limited, and it lacked radar. This aircraft was used mainly against Russian convoys, from 1942 onwards. (Philip Jarrett)

The longest-ranged German...

The longest-ranged German anti-ship aircraft was the Fw 200 Condor, used both for direct attack and for reconnaissance in support of U-boats. (Philip Jarrett)

Japanese land-based units (including seaplanes) were organised into Air Groups named after the cities at which they were based. In 1940 the Japanese created an 11th Air Fleet of medium bombers. It consisted of three Air Flotillas, each of which consisted of two or three Air Groups. In effect it was the land-based equivalent of the First Air Fleet, the carriers and their aircraft separate from the First Fleet (which included two carriers supporting the battleships directly). There were also fleets intended specifically to operate in the Mandated Islands: the Fourth and Fifth. Among their roles were attrition of any US force trying to pass through the Mandates en route to the expected decisive battle in home waters. Fourth Fleet included 24th Air Flotilla, equivalent to the three medium bomber flotillas (21st, 22nd, 23rd) of 11th Air Fleet. In addition to the attacks on the two British capital ships, aircraft of the 21st and 23rd Air Flotillas were responsible for the early attacks on the US air bases in the Philippines.

The French Navy had both a few carrier aircraft and considerable numbers of land-based torpedo bombers as well as seaplanes. Its aircraft do not figure in this book because it had few opportunities for action before France fell in 1940.

Before the war Germany had a separate naval air arm equipped with ship-based floatplanes and with larger He 115 coastal floatplanes and flying boats.⁶ Despite an agreement leaving attacks against ships to the naval air arm, the Luftwaffe created its own anti-ship unit, X Fliegerkorps, which soon absorbed the few land-based units the navy had formed. At the outbreak of war the Luftwaffe considered the torpedo inadequate compared to bombing, particularly dive or glide bombing. Torpedo attack was frowned upon as tactically difficult. In November 1940 Göring extracted from Hitler an order temporarily forbidding the provision of aerial torpedoes to anti-shipping units, in theory to allow their use in a special operation in the Mediterranean (this was soon after the Luftwaffe conducted successful torpedo trials using the He 111). The Luftwaffe did not take over development of air-launched torpedoes until 1942, by which time it was too late to develop new ones for wartime service. German aircraft were used most extensively against merchant ships between 1939 and 1941. According to a post-war study published in the BuAer Confidential Bulletin, during this period Allied losses in ships sunk, captured and severely damaged were about twice that the United States brought into the war in December 1941. In effect the 1939–41 German war on merchant shipping cost the Allies a year of new construction. Apart from mining, which peaked in November 1939, German aircraft did not attack merchant ships during 1939, due both to lack of resources and to deference to neutrals. Systematic attacks on minesweepers began in December, and attacks on merchant ships began with the invasion of the Low Countries in May 1940. During the thirteen months ending 31 May 1941, before German air assets were redirected against the Soviet Union, German aircraft sank or severely damaged 3.8 million tons of merchant ships, compared to 3.2 million for U-boats; the aircraft accounted for 1.7 million tons sunk and 2.1 million tons disabled.

The Germans made extensive use of their longest-range aircraft, Fw 200 Condors (modified pre-war airliners), against merchant ships. Because they could not dive-bomb, like Ju 87s or glide-bomb like Ju 88s, Condors had to make masthead attacks in order to score hits. Before British and other merchant ships could be armed adequately, they were effective: the Germans claimed that in the initial campaign between 15 March and 31 October 1941, bomber attacks accounted for 161 merchant ships sunk (plus one probable) and 113 damaged. This was apart from bomber attacks around the British Isles. As the merchant ships were increasingly armed, these attacks had to be abandoned, initially against convoys and then even against individual ships. Eventually the Condor was modified to attack at high-level using a computing bomb sight. These aircraft were also used for aerial mining around the western ports of the United Kingdom, and eventually to launch stand-off missiles. Their most important role was reconnaissance in support of the U-boat campaign. Success was hampered by the inability of both the U-boats and the aircraft to find their positions accurately, so that a convoy position report might be useless (the wolf packs solved the problem by creating patrol lines of submarines, but that became impossible as Allied air cover improved). The reconnaissance role became crucial after mid-1943, when the Germans lost their ability to read convoy codes. Admiral Karl Dönitz began to seek air support for the U-boat campaign almost upon gaining office as naval chief early in 1943. In February 1943 he signed a memo: air reconnaissance was now crucial. Aircraft had to penetrate to mid-Atlantic, find convoys, shadow them, and lead U-boats to them, because the existing wolf pack tactics of contacting and shadowing convoys (coupled with code-breaking) were proving less and less successful. Reconnaissance was of limited value because aircraft lacked the endurance to search large areas well out in the Atlantic: they could only fly out to a chosen position and return. Without code-breaking, there were no designated convoy positions.

According to the German navy, only in 1941 did the Luftwaffe began to accept that an anti-shipping campaign was the best weapon to use against the United Kingdom, and in the first quarter of that year it shifted its effort to attacks against British coastal targets and shipping west of Ireland. There was also a vigorous and effective aerial mining campaign. Aircraft and U-boats were integrated to an extent to oppose Allied convoys to the Soviet Union. The Germans claimed 25 per cent torpedo hits against convoys PQ16, PQ17 and PQ18. They found that it took far fewer torpedo sorties than dive bomber sorties to sink a ship: 9.8 vs 23.6 against PQ16 and 7 vs 9.2 against PQ17 (best weather for dive bombing), but 7.3 vs 24.3 against PQ18 (worst weather for dive bombing). After the war, German naval officers complained that even when they could be convinced to attack convoys, pilots generally concentrated on the larger ships, which they imagined were the more interesting targets, avoiding the escorts and the smaller, more vulnerable ships; large ones could absorb many hits without sinking.

Like Germany, the United...

Like Germany, the United Kingdom had an independent air force, but it also had a Fleet Air Arm which reverted to Admiralty control in 1939. The RAF had long been interested in anti-ship attack, both to defend distant territories and in hopes of supplanting the navy. Both roles made it interested in land-based torpedo bombers. The advent of metal-covered airframes and high-powered engines promised high performance. The Beaufort was the intended successor to the biplane Vickers Vildebeest. One is shown dropping a torpedo. Note the air tail, which is cocked up to keep the torpedo’s tail up. When it began using Beauforts against defended enemy convoys in the Mediterranean, the RAF had to learn to provide defence-suppression aircraft alongside the torpedo bombers. In many cases its resources were so badly stretched that there were few bombers, and they suffered badly. (Philip Jarrett)

The Soviet Union had a substantial naval air arm without carriers. Like the Japanese, it operated land-based bombers and its fighters defended naval bases. The bombers, of the same types operated by the land air force, were organised into Mine-Torpedo Regiments. They were expected to neutralise an enemy fleet by mining his bases and their approaches. This force was not particularly effective during the war, but the Mine-Torpedo Regiments evolved after the war into missile-firing units which the US Navy considered the most serious threat to its carriers. The shore-based naval fighters were absorbed into the Soviet national air defence arm only about 1956.

Wellingtons proved to be...

Wellingtons proved to be effective night torpedo bombers. This aircraft of 38 Squadron is shown in Egypt in 1942. Note the absence of the usual air tail. (Philip Jarrett)

The Beaufighter played several...

The Beaufighter played several important parts in the war at sea. Initially the Admiralty saw it as long-range fighter capable of covering major fleet units near enemy territory in European waters, much as it thought the Germans were using their long-range fighters to give their own capital ships freedom of action. On this basis the Admiralty convinced the Ministry of Production to keep the Beaufighter in production after the initial RAF night fighter requirement had been met. Coastal Command also wanted Beaufighters, both to protect coastal shipping and as a strike aircraft. In 1942 it began to form Strike Wings consisting of both torpedo Beaufighters (Torbeaus, shown) and anti-flak Beaufighters whose strafing runs were intended to suppress enemy air defences. This combination proved far more successful than the earlier masthead-level attacks. The success may have been due in part to the greater number of attacking aircraft involved, which helped saturate enemy air defences, and also to the relatively high speed of the Beaufighter, which also made defence more difficult. (Philip Jarrett)

Other countries had independent air arms whose interest in attacking ships was often connected with a claim that airpower made navies obsolete. The first was the Royal Air Force (RAF), founded in 1918. The associated aircraft development and production organisation was the Air Ministry, which continued in that role for both naval and land-based aircraft after the Royal Navy regained control of the Fleet Air Arm in April 1939. Thus the two services shared R&D resources such as the Royal Aeronautical Establishment (RAE). Even when the RAF controlled the Fleet Air Arm, the Admiralty paid for the aircraft and supplied many of the observers, but there was no career path comparable to that in the US Navy, from pilot to admiral. That limited the air-mindedness of the naval officer corps. Also, without its own air staff to advise it, the Admiralty could not be sure that those providing technical advice truly understood naval issues. A subtler effect of the shift to the RAF was the limited aircraft capacity of British carriers, which made it difficult to combine adequate fighter defence with powerful strike capacity.⁷ During the Second World War the RAF continued to be responsible for land-based maritime strike aircraft, although their Coastal Command came under Admiralty operational control.

The US Army Air Corps (and later the Army Air Force) considered coast defence an important role, and therefore equipped its land-based medium bombers to drop torpedoes (it had no interest, however, in dive bombing). In the South Pacific, the Army Air Corps attacked Japanese shipping, on at least one occasion (the battle of the Bismarck Sea, 2–4 March 1943) achieving considerable success with skip-bombing.

Italy had a unified air force (like the RAF), although the Royal Italian Navy retained ship-based floatplanes and seaplanes. Air unification probably prevented the navy from building the carriers it wanted during the inter-war period (it finally received permission during the Second World War, after the Royal Navy demonstrated the value of carriers).

Air Attack

Before the advent of guided weapons, an aircraft delivering an attack was, in effect, the gun launching a projectile. The pilot gave the projectile both direction and forward velocity. Accuracy depended both on how well he aimed and on how well the projectile (bomb, torpedo, later rocket) followed through. The pilot’s need to steady up on course in order to aim was the main opportunity afforded the anti-aircraft defence, since until then the pilot was more or less free to manoeuvre. Conversely, anti-aircraft fire could ruin a pilot’s aim by forcing him to manoeuvre instead of steadying on course. The only exception to the straight run was that, like its sea-launched counterpart, an aerial torpedo could, at least in theory, be set to turn (angle) after launch. This possibility seems to have been realised only by the British, the Germans, and probably the Italians.

Prior to the Second World War it was accepted that a fleet in harbour might well be subject to night attack – as at Taranto in November 1940 – but it seems to have been assumed that ships at sea would be too difficult to locate. That was not at all true on a moonlit night, as wakes could be very visible. They were often phosphorescent, too. Night attacks on moving ships at sea, which were first mounted by the Italians in the Mediterranean in 1940, changed the situation considerably. Airborne radar much simplified night attack, although blind attacks were not possible until the advent of centimetric radar, which was limited to the Allies. Night also limited fighter defence. Even in 1945 the US Navy operated special ‘night carriers’, the other carriers being limited to day aircraft. Ships’ guns were the main night fleet air defence, and they were limited by the development of radar-controlled blind fire. As late as 1945 US doctrine for night convoy air defence was to make smoke and not to fire unless attacked, because muzzle flashes would become aiming points for the enemy.

For the inter-war...

For the inter-war US Navy, the single most important aviation development was the discovery of just how many aircraft the two huge carriers Lexington and Saratoga could operate. Exercises at the Naval War College showed that numbers of aircraft were paramount, and when he became Commander of Air Squadrons of the Battle Fleet (which then had the single small experimental carrier Langley) Captain Joseph M Reeves, Jr. asked his pilots how they could operate more aircraft. They discovered that instead of striking aircraft below as they landed – as in the Royal Navy – they could have them moved forward, protected from landing aircraft by a wire barrier. That made for a much shorter interval between landings. The shorter interval supported a much larger carrier air group. This was an inherently dangerous procedure, but it worked, and it gave the US Navy considerable numerical advantages over the Royal Navy and the Imperial Japanese Navy (which followed British operating practice). Unlike the British and the Japanese, the US Navy equated aircraft capacity to the size of the flight deck, which determined how many aircraft could be parked forward during landing, or how many could be spotted aft before take-off (leaving enough of a deck run to take off). Huge US carrier air groups made the balance of air forces at Midway much closer than the ratio of carrier numbers (four to three) might otherwise suggest. Its numerical advantage in turn made the US Navy more conscious of the value of carrier fighters, because it could have both a large fighter complement and a large striking force, even of massive torpedo bombers. Once it also had radar, the fighters made an enormous difference in fleet air defence. The US operating practice did have its drawbacks, however. With the deck loaded aft for a strike, it might be difficult to recover scouts. With aircraft filling the foredeck, it might be difficult to launch them. Arresting wires were rigged at the bow as well as the stern. The carrier would steam astern to recover aircraft: Essex class carriers were designed to steam astern at 20kts on a sustained basis. To launch aircraft when the deck was full, they were given hangar-deck catapults. Neither solution was particularly happy, and the US Navy was fortunate that it learned how to operate multi-carrier Task Groups, whose extra decks were a better solution. Conversely, the Royal Navy accepted many compromises, even in aircraft performance, because it assumed that its ships could accommodate so few aircraft. When it wanted more aircraft per carrier, it adopted double hangars, with their limited head-room (which made post-war modernisation of some wartime-built ships impossible). Saratoga is shown recovering her T4M torpedo bombers in the early 1930s. Unlike later US carriers up to 1945, she had a British-style closed hangar. That in turn made gasoline vapour explosions more devastating – and one such explosion doomed her sister-ship Lexington (the Japanese closed-hangar Taiho suffered a similar fate). Later US carriers had open hangar decks, which made it possible to warm up engines on them; that in turn made for faster launching of aircraft which had to be held below because they did not fit the parking area on the flight deck (whose size was set by the required take-off run).

The one ship-killing...

The one ship-killing air weapon used during the First World War was the air-dropped torpedo, first employed by the Royal Navy and intended for mass use against the German High Seas Fleet had the war continued. This US Navy torpedo bomber has just dropped its weapon off Pensacola, 28 April 1920 – and it has porpoised. In 1922 the shore-based Torpedo and Bombing Squadron of the Atlantic Fleet successfully attacked the battleship Arkansas when she was steaming at full speed 70 miles from Norfolk. They made at least seven hits on her, and a miss hit the battleship North Dakota. This exercise demonstrated that air-launched torpedoes could be made to run straight, apparently an issue at the time.

It took time for...

It took time for navies to develop effective air-launched torpedoes and the tactics which went with them. Even then, the torpedo was by far the heaviest bomb load navies contemplated, and until the advent of engines in the 1000 and 1500hp class in the 1930s, torpedo bombers were invariably heavy and slow. The first production US Navy torpedo bomber, the T4M-1 of 1928, had a maximum speed of 114mph and required 14.1 minutes to climb to 5000ft. The Depression precluded replacement of the T4M, or even an upgrade with the new R-1820 engine, as proposed in 1931. The T4M could carry a torpedo or 1500lbs of bombs, and that became the standard for the next torpedo bomber, the Douglas Devastator. Given the combination of heavy bombing and torpedo attack in one aircraft, the inter-war US Navy assumed that carrier air strikes would mix the two types of attack, which would be combined with dive bombing by other aircraft. These T4Ms are shown on board the carrier Saratoga.

Reconnaissance was always the first step in an air attack: the sea is broad, and even a large convoy or fleet is only a small speck on it. Attackers with heavy loads had insufficient endurance for any kind of search. Instead, reconnaissance aircraft or ‘snoopers’, often cued by other intelligence, found the target and homed the attackers.⁸ Destroying a snooper might prevent an attack altogether. Since ships could generally be seen and shadowed from well beyond anti-aircraft gun range, it took fighters to deal with snoopers.⁹

Torpedo bombing

During the First World War, torpedo attack was the only form of air attack which actually sank moving ships at sea. It was practiced by both the British and the Germans, and in 1918 the British planned a mass torpedo attack against the German High Seas Fleet in harbour, to be mounted from aircraft carriers. The war ended before the plan could be executed.

To be effective a torpedo had to be relatively massive. Until the Second World War, engines suitable for carrier aircraft were not powerful enough to give a large enough aircraft an impressive performance. In the early 1930s the US Navy nearly abandoned the torpedo as an air weapon, reversing its position only with the advent of the Douglas TBD-1 Devastator – whose performance might have seemed sparkling in 1936, but was decidedly unimpressive a few years later. High bomber performance introduced a new problem. A torpedo dropped at high speed from a relatively high altitude typically oscillated as it fell towards the water. If it hit the water at the wrong angle, it would dive and it might also roll. A roll would cause its elevators, which were set to make it rise out of its initial dive, to act as rudders and cause it to hook. Something had to be done to stabilise the torpedo in flight so that it hit the water at the desired angle. The solutions were air tails which guided a torpedo into the water at the right angle, often coupled with breakaway protection for the nose of the torpedo.¹⁰ Relatively few wartime photographs show air tails of any type; presumably each user considered the concept secret.

The Regia Aeronautica, the...

The Regia Aeronautica, the Italian Royal Air Force, developed torpedo tactics before the war, but in line with its view that air power was general-purpose it did not form specialised torpedo bomber squadrons. The primary torpedo bomber was the Savoia-Marchetti SM 79 Sparviero, which could carry two torpedoes, as shown, although in practice they typically carried one. After SM 79s made successful torpedo attacks in 1940, special torpedo attack squadrons, the Aerosiluranti (Siluranti were torpedoes), were formed. They received enormous wartime publicity. (Philip Jarrett)

Throughout the mid-1930s...

Throughout the mid-1930s carrier aircraft capable of lifting and carrying torpedoes had to be so large that they could not match dive bomber performance. For a time the US Navy planned to drop them altogether in favour of total reliance on dive bombers (the carrier Ranger was built without torpedo stowage). The fleet recommended not only elimination of torpedoes but restriction to two 500lb bombs for horizontal bombers; in 1932–4 BuAer retained both because it considered the performance penalties involved in carrying a torpedo or a third bomb were negligible. When it sketched a design prior to opening a new bomber competition in 1934, BuAer found that biplane configuration would limit it to 170mph, whereas a monoplane could reach 186mph; it included speed in the specification it released in 1934. This competition in effect saved the aerial torpedo in the US Navy, because it produced a torpedo bomber with high enough performance to have a reasonable chance of surviving enemy fighters: the Douglas Devastator. The rules of the 1934 competition embodied the speed BuAer estimated such an aircraft could reach; the Devastator actually made 206mph, and it proved remarkably free of mechanical defects. As a result, 114 were immediately ordered. Had the Devastator not been developed, further US carriers would probably have been built without torpedo stowage, their attackers limited to dive bombing. It would have been effective