03/31/2022. Remarks by Johan Visschedijk: "In an effort to reduce helicopter noise-production, Sikorsky modified this USN helicopter at the manufacturers' Stratford, Connecticut plant. The modifications were aimed at the helicopter's principal noise-generating components, the powerplant and rotor blades.

The intakes and exhausts of the turbine engines were fitted with specially designed mufflers, while the SH-3As five-bladed main rotor was replaced by a six-bladed one. The added blade reduces blade loading and angle of attack. Main rotor blades were designed with twisted trapezoidal tips to improve vortex flow. These changes permitted the rotor to operate at 90% of its normal speed, thus reducing the air-flow disturbances which create rotor noise. The tail rotor, fitted with ten blades instead of its original five, operated at 33% below its normal speed, producing similar reductions in airflow disturbance.

Subsequently the modified SH-3A went to the NASA facility at Wallops Island, Virginia for further tests. Results must have been disappointing or modification too costly, because it was not introduced on production models."