On the 18th January 1918 the first Mark V tank was driven out of the Metropolitan Carriage, Wagon and Finance Company factory in Birmingham. Just 10 weeks later in early April 8th Battalion Tank Corps began training with the new tank at Humieres. It was a significant step forward from their old Mark IVs.
From the outside there’s little to distinguish a Mark V tank from its predecessors, and a cursory glance at their specifications doesn’t reveal any major changes either.
The tank still weighed around 29 tons and had a crew of 8. Physical size and armament was unchanged.
However the Mark V was 1mph faster at 4.6mph, had a range of 45 miles over 35 and featured 14mm thick frontal armour rather than 12mm. A total of 400 would be built, 200 Males and 200 Females.
Although it was very much an evolution from what had come before, if we look a little deeper we find a much more capable and useful machine that played a key role in the British victories of the final months of the First World War.
New Engine and Steering
The most significant improvements concerned the engine and drivetrain. The Daimler 105hp engine that had powered all previous British tanks was clearly underpowered, but the firm weren’t able spare any resources to upgrade it as they were committed to building aircraft engines.
For the Mark V engineer Harry Ricardo was contracted to design a more powerful replacement that could fit in the same footprint inside the tank. He succeeded, his new engine could produce 150hp.
It was connected to a radically different transmission and steering system. This made use of epicyclic gears to accelerate and brake the tracks. On a human level all that was necessary to steer a Mark V was for the driver to pull back on one or other steering lever.
Doing this operated reaction brakes on the gears connected to that track. This disconnected the drive on that side, slowing the track. Power was maintained to the other track, so the tank would swing round.
This was much more straightforward to operate than the previous system that needed four men, a primary and secondary gearbox and could only be done whilst the tank was stopped. The practical effect of this was that the Mark V could be steered whilst moving. Unlike the 1mph increase in top speed over the Mark IV, this doesn’t really show up in paper specifications, but it’s arguably much more significant. It made the Mark V far more manoeuvrable, and therefore useful, on the battlefield.
The new steering system removed the need for a massive differential housing at the back of the fighting compartment. This made the rear bulkhead of the tank accessible, so it was fitted with large hatches in the roof, a door and a machine gun mount. The crew could now fire in all directions, although blind spots still existed.
Most importantly, the new system reduced the number of men needed to drive the tank from four to one, although Mark Vs kept the eight man crew. One man was designated Secondary Driver, the others could act as signallers, observers, gunners or mechanics as needed. The commander had been the fourth driver; he was now freed up to focus on leadership.
On the Mark IV the commander had to sit beside the driver. Now he could move to the best location for his role. This was in the middle, just behind the engine, where a large raised cab was attached to the roof.
This rear cab acted as an early form of commander’s cupola. It gave him a raised position to observe the battlefield and attempt to communicate with other units. A semaphore system was installed for this purpose, although how much it was actually used is unclear. The rear cab was also used to help keep the tank moving. The side panels could be opened, which allowed the crew to attach the unditching beam to the tracks. On the Mark IV doing this had required crewmen to get out of the tank and climb onto the roof, quite probably under German fire, which, since the tank was immobilised, would likely be very accurate. The cab allowed them to remain in the relative safety of the tank.
Along with the rear cab, the louvred panels behind the sponsons are the easiest ways to identify a Mark V (another is that the two visors in the front cab are different sizes). They covered the radiator cooling system. Air was drawn in on the left, passed through ducting to the radiator then was expelled on the right. This was a new design, Mark IVs had drawn air for the radiator in through the fighting compartment, which had helped provide some form of ventilation for the crew.
Whilst the new design provided effective cooling, it meant fumes and carbon monoxide would build up in the fighting compartment. The result was another difference from the Mark IV: conditions for the crew were much worse. Shutters were eventually added to the ducting to force some of the airflow through the fighting compartment, and this seems to have helped.
The Mark V and its variant the Mark V* were the mainstay of the Tank Corps throughout the Hundred Days Offensive that led to victory for the Allies. We’ll look at some of the battles of this offensive on this blog.