RH-3 Sea King Minesweeping Helicopter
In October 1962 the Chief of Naval Operations directed that a few helicopters be converted for the Airborne Mine Countermeasures (AMCM) mission for use in a mine countermeasures development and training program and eventual assignment to fleet squadrons. The twin-turbine, tandem rotor Boeing-Vertol HRB-1 or RH-46A was initially designated for this conversion. But the US Marine Corps had a more urgent need for the H-46's, so the Navy turned to the Sikorsky HSS-2 [later renamed SH-3A Sea King].
In September 1966 Naval Air Test Center pilots completed a 2 day shipboard suitability trial of the RH-3A helicopter minesweeper aboard the Ozark (MCS 2) on the open sea. This trial completed the Center's evaluation of the helicopter for the minesweeper role. The following year the ship and a helicopter detachment from newly established HC-6 were utilized in a mine countermeasures development and training program in the Atlantic Fleet and a detachment from HC-7 was prepared for training and operation on the Catskill (MCS 1) in the Pacific.
To complete its experiments with the RH-3A, the US Navy borrowed nine CH-53Ds from the Marines, fitted with devices for the detection, sweeping and neutralization of all types of mines. In 1964, Sikorsky began converting nine SH-3A's to RH-3A's for AMCM. A pivoting towboom and towhook, tension and yaw angle indicators, pilot controlled eletrical rear-view mirrors, second large cargo door on the port side, reinforced cargo floor with access to tow winch below, and two aft observation bubbles were installed. In order to strenghten the helicopter for the stresses it would be placed under during towing operations, the upper forward cabin and transverse fuselage between the cargo doors, aft tub, and the tail wheel were all reinforced. Fuel and oil capacity was also increased by additional tanks installed in the cabin.
The RH-3A was an interim AMCM aircraft. The Sea King anti-torque tail rotor was never designed for the flight regime it operated in while towing. With up to 30 degrees nose down attitude while under tension, the RH-3A's tail rotor was past it's design limitations and occassionally failed. This led to increases in the diameter and chord of the tail rotor, as well as improved construction and design. Despite it's limitations and weaknesses, the Sea King proved itself as an AMCM platform until it was replaced.
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