The Achilles’ heel of the HST set working on one engine was its ability to climb gradients. Brunel had brilliant foresight when he surveyed his ‘billiard table’ route for the original route between London and Bristol. But when he moved further west and was involved with the South Devon Railway, the topography presented a whole new set of problems. Always the innovator, his preferred option for working over the severe gradients between Exeter and Plymouth was the atmospheric railway using a piston in a tube between the rails to assist forward progress by sucking trains along into a partial vacuum. Its downfall was the lack of materials and technology available at the time. The slot in the tube, which allowed the piston to be attached to the locomotive, needed an airtight flap. Leather was the state-of-the-art material in those days. The popular perception is that it was rats that were eating away at the flap, but it was probably more a case of weather extremes with frost and extreme heat causing the leather to dry out, lose its flexibility and crack. I once took my wife's best leather coat to a specialist cleaner. They baked it to death as part of their process, and it came back stiff as a board. They had to pay for a replacement. Who knows how successful the atmospheric system might have been with modern materials?
Once that scheme was abandoned, piloting of heavy services over the steeply graded sections between Newton Abbot and Plymouth became the norm. There is plenty of photographic evidence showing the more powerful GWR 4-6-0s with a smaller one attached up front. Into the early dieselisation era, the pilot loco was frequently a North British Type 2 diesel hydraulic, which became the Class 22. During my research, a photo came to light showing a Western Region Blue Pullman set working a special, being assisted up front by a Class 52 ‘Western’ as it was about the climb Hemerdon bank. There was no suggestion that it was ailing in any way, but these sets were relatively low-powered, with just 1,000hp at each end to tackle the fierce gradients ahead. Dainton, Rattery and Hemerdon were names that became synonymous with the most difficult stretches of the route across the southern edge of Dartmoor, with gradients generally steeper than 1 in 50.
When I arranged a courtesy visit from Control to Laira depot around 2000, I invited a small group of my operations colleagues to accompany me to understand some of the issues we had as a fleet engineering department in providing enough sets for service each day. For one individual, it was his first experience of the incredible views travelling along the sea wall from Dawlish towards Teignmouth. It was a fine day so no strong easterly wind caused big waves to crash into the sides of the set, something which exposed weaknesses in the new ‘Voyager’ units as they became stranded with water getting into the works. Flange squeal indicated we were about to pass through Teignmouth and turn inland to wind along the banks of the River Teign opposite Shaldon. Beyond Newton Abbot, I pointeddue to the curvature, but it was also a lot higher due to the steeply rising gradient. My aim was to emphasise how severe this part of the route was and why we needed specific rules for traversing it under degraded conditions, such as with just one engine. That included the requirement to attach an assisting loco in certain circumstances.
