tanks. In combat, these were found to be useful against other tanks, but lacking any reasonable high explosive load they were ineffective against anti-tank guns or static emplacements. Prior to the Cromwell entering combat service, the Ordnance QF 75 mm was introduced which equipped the majority of Cromwells, essentially an adapted version of the 6-pounder firing shells from the US 75 mm gun from the Sherman. This offered somewhat lower anti-tank performance than the 6-pounder, but its much larger shell provided a truly effective high explosive load.Churchill Mk IV with Ordnance QF 75 mm main gun. Several attempts had been made to further improve the firepower by fitting a more powerful gun. In parallel with development of the Cromwell and QF 75mm gun, a new Vickers High Velocity 75mm tank gun had been in development. This proved too large for the Cromwell turret ring, and left a shortage in offensive anti-tank capability. A prior requirement for a 17-pounder armed tank led to development of the A30 Cruiser Mk VIII Challenger.A30 Cruiser tank Challenger Based on the Cromwell, the hull had to be lengthened and a much larger turret set on top to allow a second loader for the 17-pounder, a requirement of the older specification believed necessary for the larger 17-pounder ammunition. The very high turret of the Challenger was considered a liability and this led to experiments with the similar A30 Avenger version, a dedicated anti-tank version with an open-top turret.A30 Avenger SPG. Conversion of the Sherman tanks to the Sherman Firefly (a Sherman tank fitted with the 17 pounder gun) was significantly faster than Challenger production however, and driven by operational needs of the Normandy invasion production of Challenger was dropped. Fireflys (and the limited number of Challengers) provided additional firepower to Cromwell and Sherman armed troops. One Firefly would be issued to each troop of Cromwells (giving three Cromwells and one Sherman Firefly).Sherman Firefly IC Hybrid Problems were encountered due to the different maintenance requirements and associated supply complication of two tank models, as well as the performance difference between Cromwell and Sherman and the Sherman's silhouette, even larger than the Challenger. The large size and obvious difference of both Challenger and Firefly made them a priority target for Axis forces. Recognising that a common low profile vehicle was required to replace the mixed fleet of Cromwell, Challenger and Firefly tanks, a new specification of tank was created. This removed Challengers need for a second loader and mounted the newer Vickers High Velocity weapon intended for Cromwell.The Comet tank: With the A34 (the General Staff specification), later named Comet, the tank designers opted to correct some of the Cromwell's flaws in armament, track design and suspension while building upon the Cromwell's main strengths, its low height, high speed and mobility. The first prototype featured a suspension without return rollers, much like the Cromwell suspension.A34 first Prototype: notice the suspension This replaced the need for Challenger and Firefly, and acted upon the experiences gained through design and early deployment of Cromwell.A34 Comet from 11th Armoured Division - Germany, 1945. Originally,