HSL

The Bell HSL (Model 61) was an American 1950s anti-submarine warfare (ASW) helicopter built by Bell Helicopter for the US Navy. The prototype first flew in 1953, but the type became obsolete during development and was found unsatisfactory upon entering service in 1957, resulting in the cancellation of the production contract; many of the 50 production aircraft were delivered directly into storage. The last HSL was retired in 1960. It was the only tandem rotor type designed by Bell.