By its given "mark", the Tank, Cruiser, Mk I (A9) was the first in a long series of "cruiser" tanks for the British Army and Commonwealth Forces. Cruiser tanks emerged from British interwar doctrine that called upon two types of tanks - cruiser tanks and infantry tanks - to work in conjunction with one another to produce a "one-two" combat punch. The infantry tanks were to be of heavier design and intended to break through enemy lines and support infantry actions. The cruiser tanks would then be sent in to exploit the gaps created and attack enemy positions from the more vulnerable flanks or rear. Throughout World War 2, the British would create an entire lineage "cruiser" tanks as well as a stable of infantry tanks - the heavy Churchill perhaps being the most famous of the latter group.
The British concern of Vickers-Armstrongs Ltd, led by Sir John Carden, began work on a new medium-class fighting tank under the program model designation of "A9". It was a conventional approach by tank design standards of the time, complete with thin track systems, a rear-mounted engine (based on an automobile breed), cannon armament further backed by defensive machine guns and a traversing turret. One key feature of the layout was its use of two smaller turrets to house machine guns - the multi-turret design approach proving quite popular in other interwar designs prior, though ultimately proving to be of dubious tactical value in the field. Much was learned during the development of previous British tank endeavors and these qualities were collected and implemented throughout the Vickers proposal. With the deteriorating situation in Europe, there was much attention now being given to strengthening the firepower of the British military.
The A9 - known formally as the "Cruiser Tank Mk I" - became the first British-designed tank to sport its main armament in a centrally positioned traversing turret. This allowed the tanker crew unfettered firing arcs from within the vehicle without having to face the entire tank in the direction of the enemy. The cannon armament utilized the then-effective British QF 2-pdr main gun able to defeat much of the available armor of the time. The A9 was ultimately a promising venture but it did hold key inherent limitations in her design that were to keep her from achieving later battlefield successes.
The 12-ton Mark tank sported conventional track systems featuring six road wheels to a track side. Of note were that the first and last road wheels were larger in diameter than the four interior pairs. The drive sprocket was mounted to the rear of the design with the track idler at the front. Three track return rollers were fitted across the top of the track span to facilitate movement. Suspension was through triple sprung bogies to allow for adequate cross-country capability. The glacis plate was well-sloped though shallow in its implementation. The driver sat at the extreme front of the hull with vision provided through a hinged, slotted panel emerging from a protruding emplacement. Two small turrets straddled this position and mounted single machine guns. Aft of the turrets was a short hull superstructure making up the fighting compartment. Fitted to the superstructure roof was the turret housing the main armament and another machine gun for anti-infantry defense. Stowage boxes were added to the sides of the vehicle. The engine was installed within a compartment at the rear. A standard operating crew for the Mark I included a driver, seated in the front center hull, the tank commander, the gunner, an ammunition handler and two machine gunners - these two personnel seated to either side of the driver and all shared the single fighting compartment of the hull. Armor protection measured just 6mm to 14mm in thickness across the vehicle's various facings.
The vehicle was armed with the 40mm (QF 2-pdr) which - though ample for early 1930s engagements - was wholly outclassed by mid-war - especially concerning the growth of German armor during the time. Nonetheless, the cannon was fitted to a traversing turret and operated by a dedicated gun layer. 100 projectiles of 40mm ammunition could be carried aboard. A coaxially-mounted .303 caliber Vickers machine gun was added next to the main gun and also operated by the gunner. Unique to the design of the Mark I tank was its use of the two additional .303 Vickers machine gun mounts - these in the forward hull to either side of the driver position in their own - albeit smaller scale - turret emplacements. As these positions were standard fixtures on the Mark I design, the tank required two dedicated machine gunners as part of the standard operating crew (in comparison, other standard combat tanks of the war required between three and five personnel). Some 3,000 rounds of .303 ammunition were carried to cover supply to all three machine guns.
The Mark I tank was powered by a single AEC 179 series 6-cylinder gasoline engine developing 150 horsepower. The engine was originally based on a standard commercially available Rolls-Royce car engine breed though this proved lacking for the design's weight and expected capabilities. The AEC was another commercially-available engine though it was of heavier-minded design origins and used to power British busses in the civilian market. Its rear-set placement also kept it at the more vulnerable rear of the tank, though far from the front of the vehicle, the area expected to take the brunt of enemy fire. Top road speeds in ideal conditions was up to 25 miles per hour with an operational range of approximately 150 miles.
Production of Mark I cruiser tanks began in 1936 and spanned into 1941 to which only 125 total vehicles were ultimately produced - all by Vickers. By this time, the British Expeditionary Force was in all-out war within a coalition of Allies in Europe against the might of the German Army. The Mark 1 design was further evolved to become the Mark I CS - a "close-support" tracked vehicle mounting a large-caliber 94mm L15 howitzer while retaining the original's running gear, engine and hull. Both Mark I modelswere used in early combat actions until, inevitably outmoded on the battlefield by evolving German armor.
As with most light-minded tracked armored vehicles used early in the war, the Mark I initially found successes, proving agile and relatively quick while her main gun armament was able to deal effectively with German and Italian armor offerings. The Mark I saw definitive combat actions at the French and Greek fronts in the Allied attempt to stem the Axis advance. Expanded combat actions also included appearances in the North African desert campaign where it proved effective enough against the early Panzer II light and Panzer III and Panzer IV medium tanks under the command of fabled German General Erwin Rommel and his Afrika Corps. These actions also proved the value and excellent design nature of the British 40mm QF 2-pdr guns as an anti-tank/anti-armor weapon.
However, the situation changed with the advent of the better-armored Panzer IVs beginning to debut in and, as such, the Mark I days were officially numbered. The Mark I, herself, lacked much in the way of inherent armor protection against German guns and her many vertical facings did little to deflect incoming projectiles. Light armor lacked against larger-caliber shaped charges and the vertical facings of the main turret, the driver's compartment and machine gun turrets acted as "shot traps" for incoming enemy projectiles landing direct hits.
The British attempted to shore up some of the issues of their Mk Is by developing the "Cruiser Tank Mk II". The type fielded heavier armor protection through bolted-on panels atop the Mk I's existing armor facings in an effort to increase the tank's survivability. The new tank retained the turreted 40mm main gun armament but did away with the dual machine turrets in the front hull. Instead, a single .303 Vickers/BESA machine gun was offset to the right-hand side. Power was again through an AEC 6-cylinder gasoline engine. The added armor, however, did much to degrade road performance - down to 16 miles per hour from the original's 25. Needless to say, the Mark II did not fare particularly well in combat at this point in the war.
The Mark I itself was dropped from frontline British Army use as soon as 1941. Some of her underlying components were, however, still utilized in the upcoming Valentine Infantry Tank beginning service in 1940 so all was not lost.