Bell's only twin-rotor helicopter, and one of the few not built by Piasecki (later Boeing-Vertol), the HSL-1 was the largest US helicopter of the day and was intended to hunt submarines and kill them with the Fairchild Petrel air-to-underwater missile.

The Navy would have rather had a twin-engined design instead of the single large radial they got. They would also have preferred a helicopter that fitted onto the elevators of their aircraft: carriers, but the HSL was too large even with its rotors folded. Vibration problems caused protracted delays to the development. The piston engine proved so noisy that accurate readings from the sonar equipment were impossible and they saw little service in that role. A few HSLs found use as minesweepers and trainers, or for spare parts.

Jim Winchester "The World's Worst Aircraft", 2005

At the end of the 1940s, it became apparent that the helicopters in the Navy's inventory were not of the size to accomplish anti-submarine warfare (ASW) missions. Thus in 1950, the US Navy launched an industrywide competition for a new helicopter to be designed specifically for the ASW role. In the following June, Bell won this competition and was awarded a contract calling for the building of three prototypes of its Model 61, to be designated XHSL-1 (BuNos 129133/129135). This four-seat machine was the first and would be the only Bell helicopter using the tandem-rotor layout. Nevertheless each of the two rotors were of the basic Bell two blades and automatic stabilising bar. The fore and aft rotors were interconnected and could be folded for carrier operations. Despite the fact that the US Navy would have preferred a twin-engined machine, the Model 61 was powered by a single 2.400hp Pratt & Whitney R-2800-50 engine installed in the centre fuselage and total fuel capacity was 425 US gal providing a flight endurance of nearly four hours. Armament was intended to include air-to-surface missiles such as the Fairchild AUM-2 Petrel, as well as a dipping ASDIC.

The HSL-1 was equipped with a Bell-developed autopilot which permitted motionless hovering for long periods. With a crew of four, comprising a pilot, a co-pilot and two sonar operators, and a maximum gross weight of over 11700kg, the Model 61 was then the biggest helicopter to be ordered into production in the United States.

For the development and production, the Bell Helicopter Division was moved from Buffalo to Fort Worth. The first XHSL-1 flew on 4 March, 1953, but development of the HSL-1, was to be long and difficult. The helicopter suffered many teething troubles, the worst being vibration. After these had been cured, carrier tests were made aboard the escort carrier USS Kula Gulf (CVE-108) in March 1955. Even if the HSL performed well in the air, its large size, even with rotor blades folded, was not compatible with the carrier's elevator. Even worse, was its very high level of noise while in stationary flight and this limited the sonar operator's capability of identifying contacts. Due to these shortcomings the first production contract calling for seventy-eight HSL-1s, including eighteen machines under MAP destined for Britain's Fleet Air Arm, was cut back to fifty (BuNo 129154/129168, 129843/129877) in July 1955. A follow-on contract for sixteen more (BuNo 140414/140429) was cancelled. The Navy ordered the Sikorsky HSS-1 "Sea Bat" instead.

Deliveries to Squadron HU-1 began in January 1957. Production models differed from the prototypes in having stabilising fins at the rear of the fuselage. Nevertheless the HSL-1 programme was not a complete failure because the Bell helicopter demonstrated interesting capabilities in the mine-sweeping role. Six HSL-1s were modified to do this and were operated by the Navy Mine Defense Laboratory in Panama City (Florida), until the end of 1960. The remaining aircraft were used for training or as spares.

A civil variant, the D-116, and two derivatives of the HSL-1 were considered under design numbers D-216 and D-238 but they remained as projects.

Unfortunately, no HSL-1 seems to have survived.

A.J.Pelletier "Bell Aircraft since 1935", 1992

The Model 61 or HSL-1 was a large tandem-rotor anti-submarine helicopter which successfully won a design competition organised by the US Navy in June 1950. Power was provided by a 2400hp Pratt & Whitney R-2800-50 engine. The first of three prototypes flew on 4 March 1953 and 50 production helicopters were built. Each carried a crew of four (made up of a pilot, co-pilot and two sonar operators) and was intended to carry lightweight homing weapons, including missiles.

M.Taylor "Jane's Encyclopedia of Aviation", 1989

Of all the many and varied tasks that helicopters have carried out during their short but busy life, one of the more important has been that of the shipboard aircraft equipped to hunt and destroy enemy submarines. The Bell HSL-1, although not a notably successful aeroplane, was nevertheless the first helicopter designed from the outset for the submarine hunter/killer role.

As the Bell Model 61, it was announced the winner of a U.S. Navy design competition in June 1950, and an evaluation batch of three XHSL-1's was ordered shortly afterwards. It was Bell's first and only design to feature a tandem rotor layout, having a Pratt & Whitney R-2800-50 radial engine mounted at the rear and driving a transmission shaft to the front pylon. Standard Bell 2-blade rotors were fitted fore and aft, with provision for folding them for stowage on board ship. The first XHSL-1 made its maiden flight on 4 March 1953.

Equipment on board the HSL-1 included electronic tracking gear and dunking sonar and its 1814kg cargo load could include bombs, depth charges or Fairchild AUM-N-2 Petrel air-to-underwater missiles. The crew was made up of a pilots and 2 sonar operators. Production orders were given for seventy-eight HSL-1's, of which eighteen were scheduled for delivery to the Fleet Air Arm under the Mutual Defense Aid Program; but the Korean war had ended by the time the XHSL-1 test programme was completed, with the result that the British machines were not delivered and those of the U.S. Navy spent most of their brief career on training duties. The HO4S, which the HSL-1 had been intended to replace, remained in service until the appearance of the HSS-1 antisubmarine version of the Sikorsky S-58.

K.Munson "Helicopters And Other Rotorcraft Since 1907", 1968

In 1950, in response to a U.S. Navy requirement, Bell was successful in gaining the contract for a new anti-submarine helicopter. The HSL-1 was radically different from any Bell design which had gone before (or which has appeared since). It used two rotors mounted at the extreme front and rear of the box-section fuselage, driven by a massive 2400hp Pratt & Whitney R-2800 engine positioned behind the main cabin section. A useful feature was the autopilot which allowed the HSL-1 to hover for extended periods on station while using its 'dunking sonar' gear. It was because of the size of the HSL-1 production effort that Bell decided to move its manufacturing plant from Buffalo, New York to its present base at Fort Worth, Texas. In fact, the HSL-1 was a disappointment with development being protracted due to vibration problems. The result was that only 50 examples were built and these were employed on testing towed minesweeping systems for much of their service career.

R.Simpson "Airlife's Helicopter and Rotorcraft", 1998

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After a three-year development period, the prototype flew on 4 March 1953. With two pilots and two sonar operators on board, it could carry 800kg of depth charges or two Petrel air-to-underwater missiles. However, trials showed that it created too much noise for effective ASW operation, and the ending of the Korean War led to cancellation of the order for 96 HSL-1s for the US Navy and 18 for the Royal Navy. Only 50 were delivered to the US Navy.

G.Apostolo "The Illustrated Encyclopedia of Helicopters", 1984

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- The HSL was powered by a more powerful engine than contemporary helicopters. This gave plenty of power but also lots of noise and vibration.

- Large fins were added to the tail to correct some stability problems found on the prototype.

- An autopilot system allowed the HSL to hover over a suspected submarine for prolonged periods while dipping its sonar in the water, even if the operators could not hear the signals.