M7 Priest

By David Doyle

The M7 Howitzer Motor Carriage, dubbed the Priest, was the most successful and widely used example of American self-propelled artillery during WWII. Examples continued to be used by the U.S. Army during the Korean war, and beyond, even serving Allied countries into the 1970s. Coined the Priest due to its pulpit-like structure for the gun commander, this armored fighting vehicle would see action in North Africa, Italy, and the D-Day landings in Normandy and all the way to Germany.

• Language: English
• Publisher: Pen and Sword
• Release date: Nov 19, 2018
• ISBN: 9781526738868

David Doyle

An avid military vehicle enthusiast whose collection includes 10 Vietnam-era vehicles, it not surprising that most of his 100+ published books focus on US military vehicles. In June 2015, he was presented the coveted Bart Vanderveen Award by the Military Vehicle Preservation Association, given in recognition of "…the individual who has contributed the most to the historic preservation of military vehicles worldwide."

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Introduction

While the US Army had made efforts to create self-propelled artillery in the waning days of the First World War, these efforts quickly stagnated following the signing of the Armistice. While hundreds of the armed vehicles had been ordered, only a few were completed prior to the end of hostilities and the subsequent cancellations.

Apart from a few experimental pieces, many based on the First World War-conceived vehicle, little effort was made by the United States to mechanize artillery until war broke out in Europe for a second time in 1939.

When the Armored Force was created in 1940, the table of organization and equipment called for an armored field artillery regiment to be a component of each armored division. To fulfill this requirement, many units were equipped with the M2 half-track towing a M1897 75mm gun. However, when Army Chief of Staff General George C. Marshall appointed Major General Jacob Devers as the second Chief of the Armored Force in August 1941, the shape of American artillery began to undergo rapid changes.

While the Chief of the Armored Force for the first year of its existence was Adna Chaffee, whose chosen branch of service was cavalry, Devers had selected artillery as his branch upon graduation from West Point in 1909. Just one month after Devers’ appointment a request for authorization to construct a 105mm Howitzer Motor Carriage was issued, and denied by the adjutant general. The next month the decision was reversed, and in October the Ordnance Committee began development of that vehicle.

Devers had advocated that this vehicle be based on the chassis of the M3 medium tank and two prototypes, designated T32, were ordered from Baldwin Locomotive Works. Owing to concerns about the development and production process, work also began on the half-track-based 105mm Howitzer Motor Carriage T19.

The Baldwin T32 featured an M2A1 105mm Howitzer as well as the top portion of its field carriage mounted inside an open-topped, box-like superstructure atop the M3 chassis. The two prototypes were shipped to Aberdeen Proving Ground, where trials indicated that some modifications were in order. Foremost of these was the lowering of the rear armor panel of the fighting compartment in order to facilitate the servicing of the piece and the cleaning of the breech.

The slightly modified first prototype, W-6010106, was then shipped to the Armored Force Board at Fort Knox for evaluation. These tests were conducted from 5 February 1942 through 8 February 1942. The tests concluded that while the T32 was superior to the T19 (which had begun testing in November 1941), further modification of the T32 design was in order.

The board recommended that the frontal armor be raised by 3in for increased protection, while at the same time advocating that the side armor be lowered by 11in to ease servicing the piece. Perhaps even more significant, the traverse of the howitzer in the T32 was 15 degrees right and 23 degrees left, but the board wanted the 15-degree left and 30-degree right traverse as offered by the standard field carriage. Aesthetically, the most significant change was the board’s request that a.50 caliber anti-aircraft machine gun be mounted either on a pintle at the rear of the vehicle or via a ring mount in a forward corner of the fighting compartment.

Technicians at Aberdeen Proving Ground modified the second prototype so that the requests of the Armored Force Board were met, including opting for the forward-mounted anti-aircraft ring mount, which would serve as the inspiration for the vehicle’s name ‘Priest’. The modified second prototype was then shipped to the American Locomotive Company (ALCO) in Schenectady, New York to serve as a model for the 600 vehicles of the type the firm had been contracted to produce.

Deliveries of production vehicles began in March 1942 when the first two off the assembly line were shipped to Aberdeen for evaluation. One was used for automotive tests, while the other was used by the Design Section for a stowage study. That study resulted in further minor changes to the design, beginning on 5 May 1942 when ammunition stowage was increased from fifty-seven to sixty-nine rounds, in part by eliminating two folding crew seats from the fighting compartment. In April 1942 the modified T32 was standardized as the M7 105mm Howitzer Motor Carriage.

As production neared the 100-vehicle mark, several changes were made to the rear of the vehicle. While initially the rear was very similar to that of the M3 medium tank, the improved vehicles had relocated engine air filters and mufflers, as well as the addition of armored vent covers on the engine deck as an aid to venting gasoline fumes.

By July 1942, after about 200 vehicles had been completed, a change was made to the tops of the rear stowage bins. Originally configured to accept external auxiliary fuel tanks, similar to those used on M3 Stuart tanks, the tops of the stowage bins featured the appropriate mounting hardware. Once this plan was abandoned, the now superfluous brackets were eliminated. This also would allow the boxes, by August, to become top-opening rather than side-opening. Also during the summer of 1942, the so-called step in the three-piece transmission housing, necessary to accommodate the 75mm mount of the M3 medium tank upon which the M7 was based, was eliminated and the notch-free three-piece transmission housing of the M4 medium tank was adopted instead.

Also used briefly during the summer of 1942 production was the one-piece transmission housing produced by Caterpillar. However, this transmission assembly was in considerable demand for M4 tank production, which along with other factors drove the bulk of M7 production to continue to use the three-piece transmission housing.

The M7 first saw combat in the hands of the British in North Africa, arriving in September 1942, and it was the British who gave the vehicle its code-name Priest. Those combat experiences, as well as those of US troops involved in Operation TORCH two months later, led to further changes in the M7 form. Beginning in January 1943, the pulpit –