In addition to Westland, S-61 is also built under license by Mitsubishi in Japan and by Agusta in Italy. The fuselage is rectangular with four narrow windows on either side. The engines are located on either side of the upper fuselage. A seven-blade main rotor is mounted between the engines. Rear fuselage sweeps up to accomodate a loading ramp.
Tail boom is very short with a swept tail fin.
A four-blade tail rotor is located on the port side of the fin with a large tailplane on the starboard side. A long fairing, containing main landing gear, is attached to either side of the lower fuselage. Tricycle landing gear is retractable. First S-65 was flown on October 14, 1964. The fuselage is wide and low with a few rectangular windows on either side.