Mk IV Tank

[David]

On 19 September 1916 - four days after the first tanks went into action - the British Commander-in-Chief, Sir Douglas Haig, gave an order for 1000 further tanks to be constructed im­mediately. (This order was rescinded three weeks later by the Army Council, but immediately reinstated by Mr Lloyd George, Secretary of State for War, who had more foresight).

Several faults had revealed themselves in the Tank, Mark I and it was desired to improve the design to eliminate some of these before going into mass production of the 100 new tanks. A small bridging order for 100 tanks of the original type, in which some improvements could be introduced during the course of production, was sanctioned by Lloyd George. This order would ensure that the factories, which were then still completing the last of the Mark I's, would be kept going until the new standard pattern was settled.

The interim vehicles, designated Tanks, Mark II and III - fifty of each - were delivered between about January and March 19 17. It was understood that these 100 tanks would be used only for training purposes and soft plates were used in their construction instead of armour plate and this was the cause of unfair criticism of the Mechanical Warfare Supply Department when some of these tanks were hurriedly gathered together for use in action in March.

The first of the tanks of the new design, Mark IV (again principally the work of Major W. G. Wilson in con­junction with Tritton of William Foster & Co.) were delivered to the Army towards the end of April 1917. Al­though superficially very much the same in appearance as the Mark Is and the same engine and transmission system was used, they did, in fact, incorporate many changes suggested by battle experience. The armour protection was improved - although the maximum thickness of 12 mm. was the same, the use of plates of this dimension was extended. The armament in the Male tanks was changed from the long 6-pdrs. (40 calibre), which were liable to damage when the tank ditched, to short 6-pdr. guns, 23 calibres long. These were mounted in modified sponsons which could (in both Male and Female version) be swung inwards for rail transport - on the Mark I the sponsons had to be unbolted - a time-consuming and heavy task.
Another armament change, although requested by the Army, turned out to be a retrograde step. This was the introduction of the Lewis machine-gun in both Male and Female tanks. This weapon had given good and reliable service with the infantry but turned out to be unsuccessful when used in tanks because the cooling jacket could not be protected and was very vulnerable to small arms fire, and the Lewis's cooling system sucked dust into the gunner's eyes. The mounting was more liable to penetration than that of the Hotchkiss and in some tanks a Hotchkiss was substituted for the Lewis in the front plate between the driver and commander. In later tanks the Hotchkiss (in a modified form with belt feed and pistol grip) was re-introduced in place of all the Lewis guns.
The crew conditions were improved by the introduction of better emergency escape hatches, better vision arrangements and a more effective cooling and ventilation system. The petrol supply for the engine was now by means of a vacuum feed system, which obviated the disadvantage in the Mark I's gravity feed, which frequently ceased to work when the tank was ditched. The petrol was carried in an armoured container at the rear outside the main hull in the Mark IV where it was less of a fire risk. The exhaust sys­tem was fitted with a silencer - which was absent in the earlier tanks. Steering tail wheels were not used in Mark IV - they had been dropped in Marks II-III and were also removed eventually from Mark Is.
The 105-b.h.p. Daimler engine was continued in use for the Mark IV to simplify production, although it was realized that the tank was under­powered. An uprated version, speeded up from 1000 r.p.m. to 1250 r.p.m. and giving 125 b.h.p. was introduced and was used for the later Mark IVs. It was found unreliable in the hands of the troops, however, and for this reason the tanks fitted with this type of engine were among those selected for conversion to tank tenders - supply-carrying tanks. To overcome the problem of the tank ditching, "torpedo spuds" were devised - a cylindrical beam attached to each track, which gave the track a better purchase on the ground and helped it to pull the tank out of the hole. This was only partly successful and was replaced by a single wide beam attached to both tracks by chains. Twin rails over the top of the hull carried the beam clear of the driver's cab. This device worked well and was continued in subsequent patterns of wartime heavy tanks.
The order for Mark IVs - the 1000 was just exceeded - was made up of 595 Female and 420 Male tanks. The pro­totype and approximately one third of the production machines were built by William Foster & Co., and the rest by the Metropolitan Carriage Wagon & Finance Co. Some of the Females were later converted into “Hermaphrodites” by having the right machine-gun sponson exchanged for a Male 6-pdr. sponson. This was to give them a weapon to use against enemy tanks, following the first engagement with German tanks in April 1918.

Mark IVs were first used in action in June 1917 and by November formed the greater part of the strength of the Tank Corps at the battle of Cambrai - commemorated as the first really successful battle for the tanks. Some continued in use until the end of the war, although by then later models with better mechanical performance and trench­crossing ability had been produced. As an experiment in trench crossing, however, a Mark IV was fitted with a “Tadpole Tail” - a mild steel extension of the rear horns which increased the span which could be traversed from 10 ft to about 14 ft. This device lacked rigidity, however, and was dropped in favour of extending the main hull of the tank, as was done in the Mark V*. A “Tadpole Tail” Mark IV was later fitted with a 6-in. trench mortar between the rear horns to experiment with close support for tanks in the attack.

For photos of the interior of a Mk IV, click here! For detail photos of the Mk IV in Brussels, click here! For info on the German use of the Mk IV, click here!
How to model the Mk IV
EMHAR produces plastic kits of the Mk IV both in 1/72 and 1/35 scale. Click here for a review of the 1/72 scale kit.
More photos of survivors
These are photos of two other surviving Mk IV Females, one of them to be found in the Australian Army Museum, (pictures courtesy of Brown Hawkins) and the other one in the Aberdeen Proving Ground in the U.S - or so I believe. More pictures will hopefullt be added pretty soon!

Mk IV replica?
This video shows a Mk IV that I believe is not a genuine WW1 Survivor, but a replica - built with love. The video shows very well the movement pattern of the Mk IV:

Mk IV Wrecks
The attrition rate of the WW1 Tanks was very high. This, combined with the fact that they were also considered to be Top Secret weapons, means that we today have more photos of destroyed Mk IV's than Mk IV's in combat. Below you can find some of these, many of which were taken in the aftermath of the Battle of Cambrai in 1917, when many knocked out Mk IV's were left in German hands. (Many of these were photographed again and again, as souvenirs.) Others are from the battlefield of Paschendaele, still more are seen as post-war monuments: