Mk IV Tank 'Hyacinth'
Ditched at Cambrai,
20 November 1917
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The Mark IV was the last in the series of British tanks that were directly based on the original Mother prototype, and was the main tank used at the battle of Cambrai, the first major success for the new weapon.
Work on the Mark IV began in October 1916. The Mark IV was similar to Mother and the Mark I, but with modifications based on combat experience.
On both Male and Female versions the sponsons were reduced in size and the bottom was changed to reduce their existing tendency to get caught in rough ground. They were placed on hinges that allowed them to be folded back into the interior of that tank to make it easier to move them by rail. The reduced height of the female sponson allowed a very large escape door to be installed below it, replacing the very small hatch on the Mark I.
The Vickers and Hotchkiss machine guns used on earlier models were replaced with Lewis guns, so that the tanks were using the same guns as the infantry. However later the Lewis guns were replaced with modified Hotchkiss guns, as the air cooled Lewis gun wasn’t as effective when operating from a very hot tank.
On the male sponsons the 6-pounders were reduced in length to 23 calibre to allow them to swing in. This also meant that they were less likely to get caught in the ground when moving, and as the gun was used with a reduced charge in the tanks compared to the naval version had little impact on the power of the shell.
The armour was constructed out of a special steel designed to be proof against the German armour piercing or ‘K’ bullets. In was 12mm thick in key areas, up from 8mm on earlier vehicles.
The fuel tanks were moved outside the armoured shell and placed in an armoured container on the rear of the vehicle, to reduce the risk of fire inside the tank. The old tanks had been smaller, and in the roof of the forward part of the tank, where they could easily be set on fire. The old system had been gravity fed, but that would no longer work, so a new vacuum pump based system was introduced. The larger 70 gallon tank gave the tank a maximum range of 35 miles on good ground.
Steel ‘spuds’ were added on every third, fifth or ninth track plate to improve traction.
A silencer was installed on the exhaust.
Internally a new cooling and ventilation system was installed and better escape hatches were added.
Many features designed for the Mark IV was introduced on the Mark II or Mark III. This included the ability to use wider tracks to improve traction. As a result the driver’s cab at the front was reduced in width. Further back a wedge shaped hatch with an armoured cover was installed,
During the development of the Mark V one Mark IV was given a Westinghouse Petrol-Electric drive and another was given the same petrol-electric drive as the French St. Chamond tank.
The Mark IV was produced on a much larger scale than any previous version of the tank. Eventually 1,015 fighting tanks (two thirds female, one third male) and 205 supply tanks were built, for a total of 1,220, and production lasted until May 1918. This went beyond Haig’s demand for 1,000 tanks.
In order to allow for this scale of production the two existing tank builders, Fosters of Lincoln and Metropolitan, were joined by Armstrong-Whitworth at Newcastle, Beardmores, the Coventry Ordnance Works and Mirless Watson & Co of Glasgow.
Combat
The first Mark IV was produced in 1917. It saw combat at the battle of Messines, the third battle of Ypres and the first battle of Cambrai late in 1917. During 1918 it was replaced by the Mark V.
The first Mark IVs reached France in May 1917, and were issued to A and B Battalions of the Heavy Branch of the Machine Gun Corps, the units that hadn’t been involved in the fighting at Arras. F and G Battalions also moved out to France ready to take part in the attack on Messines Ridge. Each Battalion was issued with 36 Mark IV tanks organised into three companies of twelve, two reserve tanks and six Supply Tanks (at this point old Mark I and Mark II tanks). The tanks didn’t play much of a role in the battle of Messines Ridge, but for once that was because the infantry attack was such a success that they weren’t able to catch up with the Germans!
On 28 July 1917 the Heavy Branch officially became the Tank Corps. This move came just before the start of the Third Battle of Ypres, a conflict in which the tank did not perform well. The muddy nature of the Ypres battlefield simply didn’t suit the tanks, and many simply got bogged down in the mud, unable to move on. On occasion the tanks were able to perform well, such as on 18 August when a force of eleven tanks helped capture the village of St. Julien with impressively low losses, but these examples were few and far between.
In the aftermath of the Third Battle of Ypres the Tank Corps was in urgent need of a success. They suggesting carrying out a raid in the Cambrai area, using around 200 tanks to break into the German lines, cause chaos then withdraw. Cambrai was chosen at it was an area of well drained chalk downland, as yet largely undamaged by artillery, and considered to be ideal ‘tank country’. Haig wasn’t interested in the idea of a raid, but instead enlarged it into a full scale battle. However he was willing to led the planning be led by the tank corps. The new aim was to create a breakthrough to the north-west of Cambrai, and use it to advance towards Valenciennes.
The battle would involve all nine tank battalions in France, split into three brigades, supported by six infantry divisions. There was also a cavalry corps, which was to take advantage of any breakthrough. There would be no long artillery bombardment in order to preserve surprise. A great deal of effort went into planning the attack, including training with the infantry. However individual division commanders could still alter the plans. Major General G.M. Harper, commander of the 51st (Highland) Division, used that right to totally alter the plan, ordering his men to stay away from the tanks instead of following them, and organising the tanks according to his own ideas.
A total of 378 fighting tanks, 54 supply tanks or gun carriers, 9 wireless tanks, 32 wire cutting tanks, 2 bridging tanks and 1 tank carrying telephone cables were allocated to the battle. Many of the tanks carried fascines, bundles of brushwood that were to be dropped into wider trenches to allow the tanks to cross.
The attack began early on 20 November, and was a famous success. Along a front of 6 miles the British broke through the German lines, in some places reaching as far as 4 or 5 miles past the lines. The use of massed tanks on a well chosen battlefield had been a great success, and this triumph helped secure the future of the tank. However there were failures on the first day, most notably on the 51st Division front, where many tanks were knocked out and the attack stalled. Church bells were rung in Britain to mark the sucesss. However over the next few days the attack was pushed too far, many tanks were knocked out, and the Germans prepared for a counterattack. When this came it pushed the British back out of much of the area they had captured, and the battle ended with the line roughly back where it had started. However the initial attack had proved that the tank could play a major role in warfare when used correctly.
In November 1917 in Palestine a small force of tanks took part in the Third Battle of Gaza. This was made up of three Mark IV Tanks that had arrived during the year, and surviving Mark I Tanks that had fought at the second battle of Gaza. The tanks operated in pairs, and took part in the fighting around Gaza, on the left of the Allied lines. This was the more static part of the battle – the tanks wouldn’t have been fast enough to take part in the breakthrough battle further to the east, at Beersheba. Two were badly damaged, although one of these was repaired and the other used for training. This was the last time the tanks went into action in Palestine – they weren’t mobile enough to take part in the later battles.
The Mark IV was still the main British tank during the German spring offensives of 1918. Groups of tanks were posted at a distance behind the lines, ready to move towards any breakthough. The 4th Battalion was moved south, and found itself in the way of the first German offensive. The plan was to use a ‘Savage Rabbit’ tactic, where some of the tanks would camouflage themselves close to the front, wait for the German storm troopers to move close and then ambush them. The rest of the battalion was based further back, ready to move to the threatened area. When the attack began on 21 March some of the Savage Rabbit forces were overwhelmed before they could get into action. Others did do some damage, but they mostly ran out of fuel and had to be abandoned. The 5th Battalion, further to the south, lost most of its tanks when a bridge at Brie was blown while they were still on the wrong side.
The first tank-vs-tank battle came on 24 April 1918 at Villers-Bretonneux, where a force of German A7Vs supported an infantry attack. On the British side two Mark IV females and one Mark IV Male were carrying out the Savage Rabbit role in the Bois de l’Abbe, east of the town. These three tanks were soon engaged with three of the German tanks. The two females were forced to withdraw, leaving the Mark IV Male No.4066 and A7V Nixe to fight it out. Nixe was hit and the crew bailed out, but a shell then hit the Mark IV in the tracks, disabling it. The crew of Nixe returned to their vehicle and attempted to withdraw, but it then broke down. A force of seven Whippets then arrived, and broke up the German infantry attack. One Whippet was lost, probably hit by an A7V.
German Service
The Germans captured a number of Mark IVs intact and took them into their own service. The first German tank action came on 21 March 1918 during their attack on St. Quentin on the Somme, when five captured Mark IV Females and five German A7Vs were used. The Mark IV wasn’t capable of keeping up with the German stormtroopers this early in the battle, and they were soon left behind. The faster A7Vs did a little better, but only two of them reached combat and eventually had to withdraw when the ground got too rough for them. The Germans continued to use captured Mark IVs and Mark Vs in combat, actually using them in larger numbers than the A7V. However they were never available in large enough numbers to make a difference, and the Germans had no supply of spare parts other than captured tanks.
Mark IV Supply Tank
When the Mark IV was replaced by the Mark V, many were converted into supply tanks. The sponsons were replaced with mild steel supply storing boxes. A more powerful 125hp Daimler engine was installed. They still retained a single Lewis gun. They were ordered into production in July 1917 and were used to carry small arms ammo, shells and grenades to the front and the wounded back.
Mark IV Tadpole Tank
The Tadpole was lengthened by added two 9ft long steel horns to the rear of the track framework. This required the addition of 28 more track shoes and a longer final drive, and was designed to improve the tank’s trench crossing abilities.
One Tadpole was given a platform between these long rear horns, which was used to carry a forward firing 6in mortar.
Mark IV Hermaphrodite
After the Germans began to field their own tanks and captured Allied vehicles the all-machine gun armed Female tanks became more vulnerable. One response was to give some of the Mk IV and Mk V Females one Male sponson with a 6-pounder gun.
Mark IV Fascine Tank
The Mark IV Fascine Tank was produced to carry bundles of brushwood 10ft long by 4ft 6in wide forward to fill the wide German trenches of the Hindenburg Line. The fascines were carried on the un-ditching rails carried above the cab, and could be released by the driver. Hexagonal shaped wooden cribs and steel cribs were also used for the same purpose.
Names
Stats
Production:
Hull Length: 26.4ft
Hull Width: 12.84ft (male); 10.5ft (female)
Height: 8.17ft
Crew: 8
Weight: 28 tons (male), 27 tons (female)
Engine: 105hp Daimler-Foster gasoline engine
Max Speed: 3.7mph
Max Range:
Armament (Male): Two 6-pounder guns and four machine guns
Armament (Female): Five machine guns
Armour: 6-12mm
Mark IV Male Tank from the right 
Left sponson of Mark IV Male Tank
Mark IV Male Tank from the back-right 
Right Sponson of Mark IV Heavy Tank