The tank MK I – an infant giant

by Chris Chant on 11/04/2011

Tank MK IWhatever its theoretical and technical antecedents, the tank first appeared as a practical weapon in World War I, and in its initial forms was a true child of that grim conflict. In the first weeks of their war against the Western Allies, the Germans had carried all before them in a huge sweeping offensive into north-eastern France. But then their reliance on horse transport, and the sheer exhaustion of so great and so rapid an advance told on the German infantry: the all-important right wing found by the German 1st Army over the Marne river to the east of Paris rather than over the Seine river to the west of the French capital. The Germans had been forced to deviate from Generalfeldmarschall Alfred Graf von Schlieffen’s master plan, and in the 1st Battle of the Marne (5/10 September 1914) the Allies inflicted a first major reverse on the Germans, who recoiled to the line of the Aisne river slightly to the north. The exhausted Allies were slow to pursue their initial advantage, and failed to dislodge the Germans from their extemporised positions along the Aisne river (15/18 September 1914). Thereafter each side sought to find the other’s exposed northern flank in a northward extension of the front generally known as the Race to the Sea. By 24 November 1914 both sides had reached the southern coast of the English Channel in the vicinity of Nieuport, and after a furious 10-day general offensive by the Allies between Verdun and Nieuport it became clear that operations of a fluid nature were now impossible on the Western Front, at least in the short term. The opposing sides were located in entrenched positions between the English Channel and the Swiss frontier, busy digging themselves in and shielding their positions with barbed-wire entanglements covered by machine-gun posts and field artillery.

The generals could see no alternative but to enter into a slugging match in which increasingly huge artillery bombardments were used to destroy the barbed wire and the machine-gun posts so that the infantry could storm forward as soon as the barrage lifted. The fallacy of this concept became abundantly clear as 1915 progressed. The artillery barrage revealed the location of an impending offensive, allowing the enemy to muster his reserves behind the front in the relevant sector; at the same time the barrage inevitably failed to cut more than a slight proportion of the wire, and churned up the area so badly that infantry advances were slow and fragmented; the barrages generally failed to achieve more than superficial destruction of the enemy’s system of interlocking trenches and machine-gun posts; and finally the lifting of the barrage provided the enemy with the tactical warning that allowed his men to emerge from their bunkers, man their firing positions and, perhaps most importantly, crew the machine-guns posts sited to pour enfilading and then defilading fire on the attacking infantry. Battle after ghastly battle proved during 1915 that the technology of the period could, on the one hand, rapidly strengthen trench systems but, on the other hand, provide no easy means to defeat the combination of barbed wire and machine-gun. And the poverty of the period’s military leadership could see no alternative to these head-first offensives designed to puncture the enemy’s front line and allow the cavalry to stream through into the enemy’s rear areas and exploit the breakthrough in preparation for the following infantry.

The roll call of disastrous failures in 1915 makes sorry reading: Artois, Champagne, Woevre, 2nd Ypres, 2nd Artois (Festubert, Souchez and Vimy Ridge), 2nd Champagne, and 3rd Artois (2nd Vimy Ridge and Loos) were grisly battles in which the Allies lost hundreds of thousands of men in battering ram efforts to break through the steadily solidifying German line. Gains were indeed made, but these gains were measured in hundreds of yards only, and never once was there any chance of a genuine breakthrough and the unleashing of the cavalry. As the year progressed the chance of the anticipated breakthrough became increasingly remote, but in the absence of any alternative the generals still pinned their faith in its occurrence. Another problem that they failed to consider was the nature of any breakthrough: even if the cavalry had been introduced through a rupture in the enemy’s line, it is hard to see what success it could have achieved even with the unlikely support of the plodding infantry.

E. SwintonThe concept of a caterpillar-tracked ‘landship’ had enjoyed a considerable currency in the period leading up to World War I, but failed to find any measure of acceptance among military leaders with little or no knowledge or even appreciation of science and technology: indeed, many of the combatant nations’ senior generals were still trying to come to grips with the nature and effect of established technology as epitomised by modern artillery and the machine-gun. One British convert of singular importance, however, was Lieutenant Colonel E. W. Swinton, assistant secretary of the Committee of Imperial Defence. Serving in France as a reporter during 1914, Swinton soon appreciated that his existing fears about the machine-gun’s role in defensive warfare had been more than fully realised. However, he also saw the Holt caterpillar tractors being used as tow vehicles for heavy artillery, and envisaged the possibility of fitting such tractors with armoured bodies for the transport of assault parties (or light artillery) through no-man’s land and over the barbed wire for direct assaults on the machine-guns that tore apart every infantry assault. Swinton reported back to his immediate superior, Lieutenant Colonel Maurice Hankey, the secretary of the Committee of Imperial Defence, who passed on Swinton’s notions to the Imperial General Staff and to Lord Kitchener. The IGS and Kitchener rebuffed the concept immediately, mostly on the grounds that any such ‘Trojan horse’ would be catastrophically vulnerable to artillery fire. To a certain extent the authorities were correct, for Swinton’s concept envisaged a massive machine able to transport some 50 men. What the pundits ignored, however, was the difficulty for the artillery of the period in engaging a moving target at all except the closest direct-fire ranges, which would themselves leave the artillery hopelessly exposed to counter-battery fire.

The problem faced by Swinton and other advocates of the embryonic tank concept was how to convince their sceptical superiors about the technical feasibility and tactical advantages of their novel concept. The decisive moment was perhaps the Christmas period of 1914 when, in a memorandum on the progress of the war to date, Hankey included amongst his recommendations the desirability of some sort of armoured protection for infantry assaults. The memorandum was circulated within the Committee of Imperial Defence, which numbered amongst its members the First Lord of the Admiralty, Mr Winston Churchill. Ambitious for himself and for the service whose political fortunes he controlled, Churchill was an unorthodox thinker ready to accept and develop apparently impossible ideas. Hankey’s interim recommendation therefore found a ready home with Churchill, who was already aware of the limited progress being made by the Royal Naval Air Service in the development and procurement of armoured vehicles for use in northern France and Belgium by the Naval Armoured Car Division.

Churchill responded to the Hankey memorandum with a note of his own to Prime Minister Herbert Asquith criticising the army’s apparent antipathy towards the notion of trench assault by the use of special cross-country vehicles carrying armour protection. Churchill warned, in typical fashion, that the Germans might already be working along the lines eschewed by the War Office, and urged the creation of a committee ‘of engineer officers and other experts’ to consider the concept of cross-country armoured vehicles. Asquith was impressed by Churchill’s arguments (and indeed deliberately raised fear that the Germans might already be at work on the suggested lines, when there was no evidence either direct or indirect for this fear) and induced Kitchener to order such a committee into existence.

The committee comprised the War Office’s directors of fortification, artillery and transport, and was tasked with a thorough evaluation of the suggestions made by Swinton and others. On 17 February 1915 the committee witnessed trials with a Holt tractor towing a trailer ballasted to simulate the weight of men, guns and armour: Swinton had never proposed so unwieldy an arrangement, and in extremely wet conditions the trial was judged a failure. The committee therefore reported negatively, on the grounds that the trialled system was too unwieldy and thus vulnerable, going on to claim that in any event the war would have ended before a practical system could be evolved. Having fulfilled the wishes of the politicians, the army allowed any current interest in the concept to lapse.

The torch now passed to the Royal Navy in the form of the RNAS, which was already using powerful touring cars fitted with armour and machine-guns for the mobile defence of its air bases at Calais and Dunkirk. These vehicles were very limited by their origins, but the value of armour protection was sufficiently impressive for the RNAS commander, Captain Murray Sueter, to urge upon Churchill the potential armoured vehicles based on the Diplock Pedrail crawler chassis for greater cross-country mobility. The RNAS was alive with interesting concepts at this time: one of the most ambitious was proposed by Flight Commander Thomas Hetherington, transport officer of the RNAS Armoured Car Division, as a ‘land battleship’ based on a tricycle chassis whose 800-hp (596.5-kW) diesel powerplant was to drive three 40-ft (12.2-m) diameter wheels to allow this massive machine to cross German trenches, which were 2.75 m (9 ft) wide. The ‘land battleship’ was to carry prodigious armament in the form of three turrets each fitted with two 4-in (102-mm) naval guns.

Such a machine was clearly impractical, but on 15 February 1915 Hetherington was called to describe his concept to a receptive Churchill. Full of enthusiasm, the First Lord of the Admiralty ordered the establishment on 20 February of a Landship Committee under the chairmanship of Mr Eustace Tennyson d’Eyncourt, the Director of Naval Construction. The committee included Hetherington and a number of engineer and transport specialists, with Lieutenant Albert Stern as its secretary, and its initial brief was the assessment of the two different ‘landship’ concepts embodied in Sueter’s tracked and Hetherington’s big-wheel notions. While the committee was still assessing the two options the impetuous Churchill on 26 March ordered prototypes of the two types in the form of 12 tracked and six wheeled machines, the latter sensibly scaled down with 15-ft (4.57-m) diameter wheels. The development of the tracked type was entrusted to Colonel Crompton, a highly capable though elderly engineer with a wealth of transport experience, aided by Lieutenant W. G. Wilson of the RNAS armoured car force and a pre-war automotive engineer of great repute. The big-wheel type was contracted to a Lincoln firm, William Foster and Co. Ltd under the managing directorship of Mr William Tritton: the company’s Foster-Daimler petrol-engined tractors were already in service with the Royal Marine Artillery as heavy gun tractors, and it was thought that the mechanical system and other components of these vehicles could be adapted for the proposed big-wheel machine.

One of the initial conclusions of the Crompton team was that the Diplock Pedrail could not be used as the basis of a machine for service in France as its length of more than 40 ft (12.2 m) made it too unwieldy to negotiate the types of bend commonly encountered on French roads and, perhaps more importantly, country lanes. At the same time it was also appreciated that the Diplock Pedrail was mechanically complex and considerably underpowered. Work on adaptation of the first chassis was abandoned in May 1915, and the chassis was handed over to the army, which also abandoned the type.

The Crompton team deemed that an articulated chassis would be needed for a machine able to operate in France, and after trials with an ex-agricultural machine on Greenhithe marshes an order was placed in the USA for two Bullock Creeping Grip Caterpillar tractors. It was appreciated that the Bullock machine was too small to provide the 5-ft (1.52-m) trench-crossing and 2.5-ft (0.76-m) parapet-climbing capabilities fixed as minima by the Landship Committee, so at the same time additional track and suspension components were ordered so that larger machines could be developed. The two Bullocks were delivered in June 1915 to the new RNAS testing ground at Burton-on-Trent, where Wilson was in command of the test programme.

Meanwhile the Foster company had completed its mock-up of the big-wheel proposal. It was abundantly clear that the machine was too big and ponderous to have any real tactical value, and would moreover be a considerable target for artillery. In May 1915 the big-wheel concept was formally abandoned, and all development effort was henceforward devoted to the tracked machine. Early trials with the Bullock machine were essentially encouraging, but realistic assessment indicated that the vehicle was still too unhandy for France and, moreover, that the coupling between the two major units was too weak for service use, especially for tasks such as trench crossing.

No. 1 Lincoln MachineMeanwhile Swinton had been working to overcome the army’s inertia so far as armoured vehicles was concerned. Although at first his efforts met the wall of refusal engendered by the field army’s chief adviser on military engineering, dividends were finally paid by his close links with the head of the newly created Inventions Department of the Ministry of Munitions (headed by Mr David Lloyd George, who was becomingly increasingly distraught with the level of casualties in France): renewed army interest was finally evinced. At the same time a GHQ officer in France, Major Glyn, had been sufficiently impressed with Swinton’s initial approach to press for army liaison with the Landship Committee. The ball was tossed backwards and forwards in typical fashion before it was decided at the end of June to invite four army representatives onto the Landship Committee, which thus became a joint-service body with the army’s Director of Fortifications as chairman. A number of RNAS personnel were transferred to the army to ease the task of bringing the new type of weapon to fruition. Additional impetus was given to the work by an about-turn in the attitude of GHQ in France, which now saw the new machine as offering a sensible alternative to the head-on artillery and infantry assaults that were continuously proving themselves such costly failures.

In this time Swinton had been evolving his particular concept, formalised in a series of memoranda reflecting the demands of a front-line machine. These thoughts were combined into a specification issued on 9 June for a machine with the following characteristics: a 4-mph (6.4-km/h) maximum speed on flat ground, a 20-mile (32-km) radius of action, the ability to make a sharp turn at maximum speed, a reversing capability, the ability to climb a 5-ft (1.52-m) parapet with a 1-in-1 slope, the ability to cross an 8-ft (2.44-m) trench), a crew of 10, and an armament of one light quick-firing gun and two machine-guns. Swinton also called for armour up to 12 mm (0.47 in) thick, and ultimately a 6-pdr (57-mm) naval gun rather than the 2-pdr (40-mm) pom-pom originally envisaged as the main armament.

The Landship Committee had now decided to end further exploration of the articulated chassis in favour of a new vehicle roughly equivalent to one half of the articulated machine, but engineered for the specific military demands of service on the Western Front. On 22 July (confirmed on 24 July) the work was entrusted to the Foster company, under the design leadership of Tritton with Wilson as his deputy and the Landship Committee’s representative. This vehicle was to use the lengthened Bullock tracks and additional suspension units ordered during May in combination with the standard 105-hp (78.3-kW) Foster-Daimler petrol engine.

At last real progress could be made and the new prototype, variously known as the Tritton Machine or No.1 Lincoln Machine, was soon taking shape after the start of construction on 11 August. The vehicle emerged as a boxlike hull of boiler plate, the standard Foster’s powerplant and transmission driving the lengthened Bullock tracks low-mounted at the base of the hull on each side. Provision was made in the hull roof for a centrally mounted turret accommodating a 2-pdr (40-mm) naval gun (only a dummy turret was ever fitted), and steering was effected by a combination of differential braking and/or movement of the two 4.5-ft (1.37-m) diameter wheels projecting from the rear of the hull on a bogie frame for an overall length of 26 ft 6 in (8.08 ft) and a height of 10 ft 2 in (3.10 m). The fully laden machine turned the scales at some 32,480 lb (14733 kg), and with a crew of between four and six men could attain 3.5 mph (5.6 km/h) under favourable conditions. The No. 1 Lincoln Machine was first run on 10 September 1915, and immediately encountered problems as a result of the inadequate Bullock tracks, which were easily shed and had poor grip even in good going.

Tritton and Wilson realised that the tracks would have to be completely revised, and launched a high-priority effort to produce an effective type. Considerable experimental work was undertaken before the two men evolved a new and mechanically simpler type of track based on lengthened track frames with rollers carrying the tracks proper, each comprising cast steel shoes riveted to links fitted with guides that engaged the inside of the track frames. Fitted with this radically improved type of track the No. 1 Lincoln Machine became Little Willie, which emerged in December 1915 and immediately showed itself superior to the original: the tracks were more reliable, and allowed Little Willie to cross a 5-ft (1.52-m) trench and to climb a 4.5-ft (1.37-m) parapet: the comparable figures for the machine in its original form had been 4 ft (1.22 m) and 2 ft (0.61 m). In other respects Little Willie was similar to the No. 1 Lincoln Machine.

Little WillieLittle Willie was obsolescent even as it appeared, however, for even before the No.1 Lincoln Machine had started its trials the ingenious Wilson had come up with a notion to overcome the basic design’s lack of stability when surmounting an obstacle. Wilson’s inspired thought was to combine the parapet-climbing capability of the original big-wheel notion with the other advantages of the tracked concept: a new machine was planned on the basis of the existing hull, but with the tracks running round the full height of the hull and over ‘horns’ (projecting forward and aft from the hull on each side) to provide over the lower forward section an arc approximately equivalent to that of a 60-ft (18.3-ft) diameter wheel.

The result was the rhomboidal- or lozenge-shaped tank that became standard in World War I, combining the parapet-climbing superiority of the big-wheel concept with the trench-crossing, stability and silhouette advantages of the tracked chassis. The Landship Committee was shown a wooden mock-up of Wilson’s design at the time of the No. 1 Lincoln Machine’s trials in September. As a further aid to stability in the revised concept, the roof-mounted turret was abandoned in favour of a heavier armament located in two hull-side sponsons. The specification for the vehicle, to be called Big Willie, was settled on 29 September: frontal armour 10 mm (0.39 in) thick, side armour 8 mm (0.315 in) thick, a crew of eight (including four men for steering and gear changing), a speed of 4 mph (6.4 km/h), and a main armament of two 6-pdr (57-mm) guns backed by four 0.303-in (7.7-mm) machine-guns.

The building of the new machine was seriously hampered by labour problems at the Foster company, where the secrecy of the work was such that the men could not be given war worker badges and began to leave when they were accused of cowardice for not having volunteered for the services. During construction the machine was variously called the Wilson Machine, the Centipede and Big Willie, but finally emerged at the end of 1915 as Mother, which weighed 62,720 lb (28450 kg) and was capable of 3.7 mph (5.95 mph) on its 105-hp (78.3-kW) Foster-Daimler engine. Built of boiler plate rather than the lightweight pressed steel proposed for the production version, the machine was 32 ft 6 in (9.91 m) long including the twin steering wheels at the rear, 13 ft 9 in (4.19 m) wide over the sponsons, and 8 ft (2.44 m) high. In the front of each sponson was a naval 6-pdr (57-mm) quick-firing gun, the four machine-guns being disposed one in the rear of each sponson, one in the bow and one at the rear. Naval guns were used as the army’s Master General of the Ordnance was opposed to the tank concept and therefore refused to release any weapons for use in the new machines.

Mother first ran on 3 December 1915, at about the time that the cover name ‘water carrier’ (soon amended to ‘tank’) was ordained at Swinton’s instigation in preference to the revealing ‘landship’. After initial and successful running trials, Mother was fully completed on 26 January 1916 and moved, together with Little Willie, to Hatfield Park for two official trials and demonstrations. The first was attended only by those intimately involved in tank development, but four days later on 2 February the main demonstration was attended by such dignitaries as the Secretary of State for War (Field Marshal Lord Kitchener), the Minister of Munitions (Mr D. Lloyd George) and the Chancellor of the Exchequer (Mr R. McKenna). Both tanks were put through trials in terrain very similar to that of the Western Front (complete with British and German trench layouts), and Mother was judged worthy of production. As the Ministry of Munitions had in December refused to allow tank production, Kitchener ordered Stern to the War Office to oversee production on a direct basis, and this had the desired effect of forcing the ministry’s hand: on 12 February the ministry ordered the production of 100 tanks based on Mother (25 by Foster and the other 75 by the Metropolitan Carriage, Wagon and Finance Co.) in a programme to be overseen by the Landships Committee, now renamed the Tank Supply Committee headed by Stern and including Swinton as a member.

Churchill was now in France, having been forced to resign in May 1915 when a coalition government took over from the Liberal administration after the failure of the Dardanelles campaign, but had tried to keep up with developments. Though now ‘only’ a regimental officer, Churchill sent to Field Marshal Sir Douglas Haig, the British commander-in-chief in France, a paper entitled Variants of the Offensive which, among other items, exaggerated the state of tank development but persuaded Haig to despatch Major Hugh Elles to report personally on the new weapon. It was Elles’s approval that persuaded Haig to think in terms of an order for 40 tanks that led to the initial plan for 100 vehicles, later increased to 150 vehicles.

In March 1916 the new tank arm was formed under Swinton, initially as the Armoured Car Section, Motor Machine Gun Service and then from May as the less revealing Heavy Section, Machine Gun Corps. (After the tank had been used in action the name was changed in November 1916 to the Heavy Branch, Machine Gun Corps and finally in July 1917 to the Tank Corps.) As the men for the new branch were being found and trained, production of the service version of Mother, the Tank Mk I, was being undertaken for the first deliveries to be made in June. At first it was planned that the production model should be all but identical with Mother other than construction in mild steel rather than boiler plate and the installation of a frame of wood and chicken wire over the roof to prevent ‘bombs’ (grenades) from lodging and detonating on it. The armament sponsons projected about 3 ft (0.91 m) from each side of the tank, and were therefore designed to be removed for separate (or towed) carriage to ease transport problems. Each sponson weighed some 3,920 lb (1778 kg), and required about eight hours to remove or replace in the field with skids and levers, assuming that the hull had not been ‘wrung’ in transit and thereby moved out of alignment the bolt holes that had to be matched by those in the sponsons.

However, in April 1916 Swinton decided that a proportion of the tanks (ultimately fixed at half of the production run) should be completed with the Hotchkiss 6-pdr (57-mm) guns replaced by two machine-guns. The more powerfully armed variant was designated Tank Mk I Male, and at a combat weight of 62,720 lb (28450 kg) carried an armament of two Hotchkiss L/40 guns (each with 166 rounds) in limited-movement mountings allowing traverse out to an angle of 120° from the centreline, plus three or four Hotchkiss machine-guns (with a total of 6,272 rounds of ammunition): the role of this variant was to tackle guns, emplacements and other fixed defences. The lighter variant, turning the scales at a combat weight of 60,480 lb (27434 kg), was designated Tank Mk I Female and carried an armament of one or two Hotchkiss air-cooled machine-guns and four water-cooled Vickers machine-guns (in place of the Male’s guns and sponson-mounted machine-guns) with a total of 30,080 rounds of ammunition: the role of this variant was protection of the heavier Males from infantry attack, and pursuit of enemy infantry.

The men of the new army branch were soon coming to grips with their extraordinary new machines, which offered great things but were extremely uncomfortable: the Tank Mk I lacked any form of sprung suspension, vision of the outside world was limited by the small size of the few vision slits, the engine was unsilenced (meaning that internal communication had to be undertaken largely by hand signalling) and ventilation was virtually nonexistent. And as operations were shortly to confirm, while the tank’s construction (soft steel that was cut and drilled and then hardened before being bolted together over the primary structure of riveted girders and angle irons) may have provided protection from smalls arms fire it was totally prone to spall and splash when struck on the outside: this last meant that the crew had to wear thick clothing and face protection to avoid being pierced and cut by the shards sent flying off the inside of the armour when it was struck on the outside (spall) or hit by the molten metal that penetrated the tank’s ill-fitting plates when bullets melted on hitting the tank (splash).

The Tank Mk I had a crew of eight comprising the commander/brakesman and driver in the front with their heads in the central cupola, four gunners in the central portion, and two gearsmen in the rear section. Modest steering capability was provided by the tail in good conditions, but major course corrections required a four-man effort in which the gear driving the track on the inside of the turn was put into neutral while that on the outside was operated in first or second until the turn had been accomplished, whereupon the same drive was applied to both tracks. The steering tail increased trench-crossing capability from 10 to 11 ft 6 in (3.05 to 3.51 m), but proved a great hindrance in operations (being easily damaged or clogged with mud), and from November 1916 was abandoned. Most of the vehicles so modified were then fitted with a substantial shelf between the rear horns for the carriage of equipment such as a towing hawser.

The tank went into action for the first time on 15 September 1916 in one of the subsidiary components of the Battle of the Somme, namely the Battle of Flers-Courcelette: here the British Reserve and 4th Armies were to punch a 4-mile (6.4-km) hole in the German line at Flers and Courcelette in the sector between Thiepval and Combles, the 10 assault divisions being supported by a proposed 50 tanks. Yet such was the technical infancy of the new weapon that some 18 Tanks Mk I had broken down before the assault started, and the surviving 32 machines were allocated in penny packets (the largest mass being seven tanks) as what were in effect mobile pillboxes that could crush wire and lead the infantry into what would clearly be totally dumbfounded German positions. In the event the tanks did well, but their role was hopelessly wrong and their effect was thus small when the Battle of Flers-Courcelette fizzled out at the end of the day.

Yet the technical seed had been sown, and ideas for the appropriate tactical use of the tank soon started to sprout in the soil of north-eastern France.

Specification

Tank Mk I

Type: battle tank

Crew: 8 (commander, driver/brakesman, two gearsmen, and four gunners)

Combat weight: 62,720 lb (28450 kg) for Male and 60,480 lb (27434 kg) for Female

Dimensions: length overall with steering tail 32 ft 6 in (9.91 m) and 25 ft 5 in (7.75 m) without tail; width 8 ft 8.5 in (2.65 m) for the hull, 13 ft 9 in (4.19 m) over the sponsons for the Male and 14 ft 4 in (4.37 m) over sponsons for the Female; height 8 ft 0 in (2.44 m)

Armament: two 6-pdr (57-mm) Hotchkiss L/40 guns with 332 rounds and three/four 8-mm (0.315-in) Hotchkiss machine-guns with 6,272 rounds for Male, and four 0.303-in (7.7-mm) Vickers machine-guns and one/two 8-mm (0.312-in) Hotchkiss machine-guns with 30,080 rounds for the Female

Armour: between 6 and 12 mm (0.24 and 0.47 in)

Powerplant: one 105-hp (78.3-kW) Foster-Daimler water-cooled six-cylinder inline petrol engine with 50 Imp gal (227 litres) of fuel in two gravity-feed tanks; power was transmitted by one two-speed main gearbox and two auxiliary gearboxes to two unsprung tracks each of 90 shoes passing over 26 rollers

Performance: road speed 3.7 mph (5.95 km/h); road range 24 miles (38.6 km); fording 4 ft 6 in (1.37 m) without preparation; gradient 24%; vertical obstacle 4 ft 6 in (1.37 m); trench 11 ft 6 in (3.51 m) with steering tail; ground clearance 16 in (0.406 m)

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