Whilst the Admiralty was using the majority of the output of UK small craft yards and had options on engines built in the USA, the RAF had to look elsewhere and turned to Canada for a source of suitable craft. On the 14th November 1940 a report, which reffered to six 70ft HSLs being built in Canada, indicated thet the craft were being built by Aero-Marine-Crafts Ltd of Trenton, Canada. Trials of HSL 151 were carried out at Trenton on the 4th May 1941, however trials at Halifax of HSL 150 had revealed bad cavitation due to the propellors being of the wrong pitch. This was rectified for the trials on HSL 151 and a speed of 34 knots was achieved.
The six craft were completed and shipped to the UK, however HSL 151 was lost en route due to enemy action. The remainder arrived at Avonmouth Docks in August 1941 to be collected by RAF Ferry crews. The craft were not immediately available, however a report from the crews indicated the craft to be more spacious, both in terms of accommodation and engine room, than the previous BPB HSLs, however the interiors were very poorly finished. HSL 150 was eventually made ready for onward passage, however whilst being transferred to Calshot the generator drives all failed and the HSL had to put into Falmouth for repairs. Later the craft suffered major failures when all three of the WWI converted Liberty aero engines blew up. The HSL was towed to Yarmouth and later on to Calshot for slipping. The cause of the failure to the engines was identified when a large hole was revealed in the crankcase. Another report indicated that the engines fitted to HSL 152 were rusted solid.
Consequently the five craft were left swinging on buoys at Calshot, however when the Marine Craft Training School (MCTS) moved from Calshot to Corswall, the craft were towed to Scotland and resumed their duties of static training craft on the buoys. The craft were eventually brought on charge in 1943, over two years after they had arrived in the UK. Subsequently two craft, HSLs 150 and 155, were overhauled during which time the three Liberty engines were replaced bt twin Thornycroft RY12 engines and Meadows 1000 hp gearboxes. However even in this role they were not a success, as the planking was thin and the craft always appeared to make a lot of water.
As a direct consequence of their poor performance, the craft were disposed of after a very short time in RAF service. HSL 153 was stricken off charge and sold in June 1945, after which HSLs 152 and 155 were stricken off in October 1946, subsequently being transferred to Admiralty control for disposal with HSL 150 and 154 going to the Admiralty for disposal in May 1947.
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