The Medium Tank Mk A (also known as the "Whippet") was an armored vehicle specifically designed to exploit breaches in the battle lines created by heavier lozenge-shaped combat tanks such as the Mark I series. The Medium Tank Mk A went on to become the most successful British tank of the war and was utilized to spearhead assaults, going on to cause many German casualties in the process. Designer William Tritton was an expert in designing agricultural machinery and was assigned to work with Major Walter Gordon Wilson in producing a "caterpillar tracked" vehicle for transporting large naval guns. While working on the project, they saw a separate but equal military application of the tractor and were credited with the invention of the Medium Tank Mk A. A prototype (interestingly with a revolving turret emplacement borrowed from an Austin armored car design) was made ready in February of 1917 and underwent evaluations thereafter. An order for 200 was placed in March of 1917 to which the system was delivered for operational service in December of that year. At a later date, Tritton would go on to design the notable Mark I thru Mark V series of heavy tanks for the war effort.
The Medium Tank Mk A fulfilled a need for a fast and cheap armored vehicle to work alongside the heavy-class tanks in plugging gaps in the line while able to make deep forays behind enemy lines in turn. Crossing the wide-spanning network of trenches by tanks of The Great War proved an ever-present issue as enemy forces simply enlarged these gaps as new capable Allied tanks came online. Such obstacles proved an ongoing issue for tanker crews and tank engineers alike.
The Whippet was rather modestly armed with three to four 7.7mm Hotchkiss-brand machine guns, all supplied through 5,400 rounds of ammunition aboard. The Whippet's primary role was in countering infantry so no cannons were issued. Not having a heavy-class cannon like the British 6-pounder the Mark I series used made the Whippet more of an armored personal carrier (APC) than a true "tank". Regardless, she was categorized as a "medium tank". Propulsion was by way of 2 x 45 horsepower standard English heavy industry bus engines, one powerplant supplied for each track. Steering was accomplished by the designated driver using an automobile-style steering wheel. When turning right or left, the throttles of the two engines were increased or decreased depending on the turn required. The tank would need more power on the opposite track of the desired direction. In practice, the engines would stall if the driver took a sharp turn left or right, forcing the tank to come to an abrupt stop. As can be surmised under combat conditions, a non-moving vehicle became a "target of opportunity".
There was no turret as in a conventional tank design per se but a fixed superstructure was fitted instead. The enclosure was large enough to fit the crew of three with up to four machine guns. At times, an additional crewmen could be added for additional fire support which required the removal of one machine gun. The 7.7mm machine guns were repositioned to any one of the four gun mounts giving the tank commander some tactical flexibility. The Mk A's speed of 13 km/h (8.3mph) and range (257 km / 160 miles) proved some of the series greatest assets, her having twice the speed and range of the Mark I series heavy tank. As such, the Whippet became one of the fastest combat tanks on the battlefield and a feared presence among German infantry attempting to defend their positions.
Early actions proved the Whippet valuable as they protected the British retreats of the German Spring Offensive of 1918. In a later recorded combat instance (in fact the second ever tank-versus-tank duel), a company of seven Mk A Whippet tanks engaged two German infantry battalions numbering 800 men in the open near Cachy. The tankers killed over 400 German soldiers ultimately rendering the force destroyed. A German A7V tank inflicted one Whippet loss and another damaged in the foray but the damage to the Germans were already done.
Whippets then took part in the August 8th, 1918 Amiens offensive, breaking through the German lines and raising havoc at the German rear while destroying large numbers of artillery pieces. A Whippet tank nicknamed the "Music Box" was present among this group and roamed behind enemy lines for up to nine hours and credited with destroying an artillery battery, an infantry battalion camp and a transport column while inflicting hundreds of casualties.
Whippets were eventually used by the German Army when captured while the Red Army also made use of the tank well into the 1930's. Examples were also seen in Ireland, Canada, Japan, and South Africa. Production totaled 200 units with manufacture spanning 1917 into 1918 under the Fosters of Lincoln brand label.