The Sikorsky CH-124 Sea King (formerly CHSS-2) is a twin-engined anti-submarine warfare (ASW) helicopter designed for shipboard use by Canadian naval forces, based on the US Navy's SH-3 Sea King. Most CH-124s were assembled in Quebec by United Aircraft of Canada. The CH-124 served with the Royal Canadian Navy (RCN) and Canadian Armed Forces from 1963 to 2018. Design and development The advent of nuclear-powered submarines in the late 1950s let to the RCN assessing this new threat. While noisier than older submarines and thus detectable at longer ranges, nuclear submarines could also reach while submerged, faster than the RCN's new destroyer escort's top speed of . There were doubts that destroyers could effectively pursue and destroy such fast vessels, even when operating in pairs. During a 25 February 1959 Naval Board meeting, it was decided to counter the threat by operating helicopters from destroyers. The RCN examined the feasibility of operating ASW helicopters from small escorts, adding a temporary helicopter landing platform to the in mid-1956; successful trials were held in October 1956 using a Sikorsky HO4S-3. A larger temporary platform was fitted on the destroyer escort ; operational trials used an RCAF Sikorsky S-58, a much larger and heavier aircraft than the HO4S; these successful tests met with approval. The RCN's then current HO4S-3 utility helicopter could not operate safely in inclement weather with a heavy weapons and sensor load, which would be imperative for the ASW role; hence, a more capable aircraft was needed. Initial 1959 studies identified two helicopters that seemed suitable—the Sikorsky S-61 (HSS-2) and the Kaman K-20 (HU2K)—but neither aircraft had flown at the time, so no choice was made. After further studies concluded that the smaller Kaman would better satisfy RCN requirements, the Treasury Board approved an initial procurement of 12 HU2K helicopters for $14.5 million in December 1960. Despite this apparent setback for Sikorsky, several factors derailed Kaman's proposal. When the Naval Board held a follow-up meeting on 27 January 1961, it was revealed that the initial 12 units' asking price had nearly doubled to $23 million, only six weeks after approval from the Treasury Board. The Naval Board still endorsed the HU2K, but there were some misgivings over the sharp price increase and reports that Kaman's performance projections may be overly optimistic. The Naval Board decided to await upcoming USN sea trials of the HU2K ahead of a final decision. These