a complete set of machinery for St. Laurent, the other ships being supplied with machinery manufactured in Canada. The main turbines and machinery were of English Electric design. DDH conversion The advent of nuclear-powered attack submarines in the late 1950s prompted RCN leaders to assess the new threat they posed. Although these craft were noisier than older submarines and could therefore be detected at longer ranges, they were also capable of while submerged, which was faster than the top speed of the St. Laurents at . Some RCN leaders harbored serious doubts that the destroyers could effectively pursue and destroy such fast vessels, even when operating in pairs. During a 25 February 1959 meeting of the Naval Board, it was decided that the Navy would counter the new threat by outfitting destroyers for helicopter operation. The RCN had examined the feasibility of operating ASW helicopters from small escorts when it modified the in mid-1956 with a temporary helicopter landing platform fitted the quarterdeck. Trials held in October 1956 using a Sikorsky HO4S-3 were successful, and a larger temporary helicopter landing platform was installed in the new destroyer escort in August 1957. Operational trials were conducted using an RCAF Sikorsky S-58, a substantially larger and heavier aircraft than the HO4S, and the success of these tests led to approval of the concept. To achieve the goal, the RCN needed a helicopter capable of all-weather day-and-night operations with a heavy weapons load—capabilities the HO4S lacked—and a means to handle and secure the aircraft on the landing platform in rough seas. Trials showed landing was not the major concern: deck handling was. Manpower alone was insufficiently quick or certain in all conditions. During the 1957 trials aboard Ottawa, it had taken 30 tense minutes to secure the S-58 to the deck during nighttime operations in rough seas. The deck handling issue was addressed by the invention of the beartrap. The Navy came up with the solution, and contracted Fairey Aviation of Dartmouth, Nova Scotia, to produce it. Fairey's prototype was installed in Assiniboine during her 1962–63 conversion. By keeping the aircraft secure, the beartrap eliminated the need for deck handling from landing to the hangar, or from hangar to takeoff. In the conversion to a helicopter-carrying vessel, Assiniboine was gutted except for machinery and some forward spaces. The hull was strengthened, fuelling facilities for the helicopter and activated fin stabilizers installed. The fin