hull, greatly increasing the vehicle's freeboard, and providing buoyancy in the water. When collapsed, it would not interfere with the tank's mobility or combat effectiveness. The first tank to be experimentally fitted with a flotation screen was a redundant Tetrarch light tank provided to Straussler. Its first trial took place in June 1941 in Brent Reservoir (also known as Welsh Harp Reservoir) in north London in front of General Sir Alan Brooke (at the time General Officer-in-Command Home Forces). The reservoir had been the location where trials of the floating version of the World War I, Mark IX tank took place, 23 years earlier. Satisfactory sea trials of the Tetrarch took place in Portsmouth Harbour. A prototype of a Duplex Drive Valentine tank began trials on 21 May 1942, although it subsequently sank (during a trial in which it was subject to machine gun fire). In June 1942, permission was given by the Ministry of Supply for the manufacture of 450 Valentine DDs. It later became clear that the Sherman was more suitable for use with a screen than the Valentine and the DD screen was adapted for the Sherman by April 1943. One reason for this was that the Sherman could move in the water with its gun forward ready to fire as soon as land was reached. The Valentine was also an older and generally inferior design. Training Valentine DDs were used for training and the majority of the US, British, and Canadian DD crews did their preliminary training with them. Crews learned elementary phases of the DD equipment at Fritton Lake, on the Norfolk/Suffolk border. Here they learnt to waterproof and maintain their tanks, use Amphibious Tank Escape Apparatus, launch from mock up LCT ramps and navigate around the two and a half mile lake. After two weeks of training at Fritton, the crews moved to Stokes Bay, Gosport, Hampshire for three weeks of intensive training from landing craft. The DDs would be loaded on the hards at Stokes Bay, and launch into the Solent. They would form up in echelon, cross of water and land at Osborne Bay on the Isle of Wight. The regiments would then move to Combined Training Centres, such as at the Moray Firth in Scotland and Barafundle Bay in Wales to train with other elements and units, during which period crews incurred several losses. On 4 April 1944, Operation Smash was