The GKAT directive was followed by a more detailed specification for the V-12 with hold dimensions similar to the Antonov An-22, intended to lift major items of combat material as well as 8K67, 8K75 and 8K82 inter-continental ballistic missiles (ICBM).

Although the first use by Mil, the transverse system had been used by several of the early helicopters, including the Focke-Wulf Fw 61, Focke-Achgelis Fa 223 Drache and Kamov Ka-22 Vintokryl convertiplane.

The airframe was largely conventional, using stressed skin construction methods with high strength parts machined from solid metal blocks.

[3] At the aft end of the fuselage access to the cabin is gained by large clamshell doors and a drop down cargo ramp with inbuilt retractable support jacks.

[3] The fixed undercarriage consists of large paired main-wheel units on oleo-pneumatic levered shock absorbers mounted at the junction of a strut system supporting the rotor systems and wings and connected to the centre fuselage by a tripod strut structure with the nose-leg attached aft of the crew section.

A pair of bumper wheels are mounted at the rear of the fuselage keel and fixed support pads ensure that the cargo ramp is extended to the correct angle.

[3] The power system and wings are mounted above the centre fuselage with interconnecting shafts ensuring synchronisation of the main rotors which overlap by about 3 m (10 ft).

Roll control is by differential collective pitch change on the left and right rotors, ensuring that sufficient lift is generated to prevent inadvertent sink.

Large elevators on the tailplane help control the fuselage attitude and provide reaction to pitching moments from the wing and variation on rotor disc angle.

The cause of the oscillations proved to be a harmonic amplification of vibrations in the cockpit floor feeding back into the control column when a roll demand was input into the cyclic stick.

[3] In May–June 1971, the first prototype V-12 SSSR-21142 made a series of flights over Europe culminating in an appearance at the 29th Paris Air Show at Le Bourget wearing exhibit code H-833.