The Bell company won a Navy design competition in June 1950 for a helicopter specifically for anti-submarine warfare. This design, Bell Model 61, was the only Bell helicopter using the tandem-rotor layout; it was powered by a 2400 hp Pratt & Whitney R-2800-50 engine and was intended to carry air-to-surface missiles such as the Fairchild Petrel, as well as dipping ASDIC. Three XHSL-1 were ordered the first of these flying on March 4, 1953, followed by a production contract for 78, including 18 destined for the Britain's Fleet Air Arm.
The Forgotten Bell HSL
U. S. Navy's First All-Weather Anti-Submarine Warfare Helicopter