In WWII the British had an armour doctrine that called for two classes of tanks. Infantry tanks were just that, fairly slow well armoured with the main goal to support the infantry. The Cruiser tanks were just the opposite they compromised armour for speed and agility. This was very important during their reconnaissance roles. Using the Meteor engine the Mk. IV could attain speeds up to 52 km/h while almost gliding across the terrain on the Christie Suspension. Later models received heavier armor when it was deemed some speed should be given up for crew protection. Late in WWII there probably were more Cromwell Mk. IV in operation than any other British tank but the Churchill and the Sherman overshadowed its importance. On September 1, 1943 the 1st Czechoslovak Independent Armoured Brigade Group (CIABG) was formed. Delays with gathering vehicles and supplies delayed their departure to France until August 30, 1944. On October 6, 1944 the brigade moved north to Dunkirk that was held by German forces and under siege by British troops. The CIABG used strong armoured reconnaissance using M5A1 Stuart and Cromwells, artillery, aerial bombardment and propaganda. On May 9, 1945 the 15,500 German troops surrendered. On May 1, 1945 a symbolic 140 man unit of the CIABG raised the Czechoslovak flag at their homeland border. With the capture of Dunkirk completed the entire CIABG moved east and on May 18, 1945 they marched into Prague.