The first Mark IV tanks arrived in France in late April 1917, and were issued to units in May. This was the first British tank to be produced and used en masse, and the first where the design could incorporate lessons learned in combat.
The Mark IV stemmed from General Haig’s order for 1000 tanks, placed shortly after their first use in September 1916. Production began in March 1917. Eventually 1220 would be built. Of this 1015 were fighting tanks – 420 Males (armed with 6 pounder guns and machine guns) and 595 Females (armed solely with machine guns), with the remaining 205 being unarmed Supply Tanks.
Mechanically the Mark IV was based on the Mark I. A number of improvements were implemented but one major disadvantage remained – it still needed four men to drive it. This was clearly unsatisfactory, but a new epicyclic gearbox that allowed for a single driver wasn’t ready until March 1917, too late to be fitted to the Mark IV.
Conditions for the crew didn’t change either. The tank still had no suspension and the engine still filled the tank with heat, exhaust fumes and deafening noise (although a silencer on the roof improved matters outside).
The improvements included slightly thicker armour. It was still 12mm thick at the front, but now more of the sides were protected by 8mm plate. Armour was also fitted to the petrol tank.
The Mark I had unprotected petrol tanks at the very front in the two track horns on either side of the cab. These would have been vulnerable to enemy fire even if they had been armoured. The new, protected tank was low down in the rear and, at 70 gallons, larger, giving the Mark IV a greater range. As the petrol now needed to flow uphill to reach the engine an Autovac fuel pump was installed.
The most obvious changes on the Mark IV were to the sponsons. Male examples were now bevelled on the lower surfaces to minimise contact with the ground. Female versions looked very different, they were only half height with a large door underneath.
Both types could be folded into the tank for rail transport. This was much easier and more popular than removing them as crews had to on the Mark I.
The weapons fitted changed too. The Male’s 6 pounder gun was replaced by a version with a barrel over a metre shorter. At realistic combat ranges this made no practical difference to accuracy or power, but it did mean the gun was less vulnerable to getting clogged with mud or damaged by obstacles as it traversed. The previous Hotchkiss machine guns fitted to Male tanks and the Vickers used on Females were both replaced by the Lewis gun, although combat experience showed that this wasn’t as successful a change and it would be reversed on later tanks.
The Mark IV’s combat debut came on the 7th June at Messines Ridge. We’ll take a look at this battle in a future post.
Find out more about tank development and First World War tanks in the books below.