The commanders who planned the raid on Dieppe had not envisaged such losses. This was one of the first attempts by the Western Allies on a German-held port city. As a consequence, planning from the highest ranks in preparation for the raid was minimal. Basic strategic and tactical errors were made which resulted in scores of Allied (particularly Canadian) deaths. The British developed specialist armoured vehicles for engineers to perform tasks protected by armour. While the RAF were able to keep German aircraft from the land battle and the ships, the operation showed "major deficiencies in RAF ground support techniques" and this led to the creation of an integrated tactical air force for army support. Because the tracks of most of the Churchill tanks were caught up in the shingle beach, the Allies began to study beach geology where they intended to land and adapting vehicles for them. The Allies changed their view that capturing a big port was necessary to establish a second front. The damage inflicted on a port to capture it, would make it useless afterwards. Prefabricated Mulberry harbours were to be built and towed to beaches during the invasion. Of the nearly 5,000-strong Canadian contingent, 3,367 were killed, wounded or taken prisoner, an exceptional casualty rate of 68 percent. The 1,000 British Commandos lost 247 men. The Royal Navy lost the destroyer "Berkeley" (on the return crossing, it was hit by bombs from a Fw 190 and then scuttled by "Albrighton") and 33 landing craft, suffering 550 dead and wounded. The RAF lost 106 aircraft. RAF Air Sea Rescue Services picked up around 20 pilots at the loss of three of Dover's five High Speed Launches. Among the RAF losses, six RAF aircraft had been shot down by gunners on their own side, one Typhoon was shot down by a Spitfire and two others were lost when their tails broke off (a structural issue with early Typhoons), and two Spitfires collided during the withdrawal across the Channel. The Germans suffered suffered 591 casualties, 322 fatal and 280 wounded, 48 aircraft and one patrol boat. Of the 50 US Army Rangers serving in Commando units, six were killed, seven wounded and four captured. The losses at Dieppe were claimed to be a necessary evil. Mountbatten later justified the raid by arguing that lessons learned at Dieppe in 1942 were put to good use later in the war. He later claimed, "I have no doubt that the Battle of Normandy was won on the beaches of Dieppe. For every man who died in Dieppe, at least 10 more must have been spared in Normandy in 1944."