The Yak 31 features a dual, contra-rotating rotor system with an elongated torso and an open cockpit. It is powered by two ASh-85 radial engines, and runs on diesel. It can operate at a maximum ceiling of 10,000 feet, and has a top speed of 130 miles per hour. It was designed to be able to carry both soldiers and materiel over distances quickly, and as such had an elongated body, and each side alternated between a locker and a seat. It could carry up to four squads of soldiers and their equipment, as well as two GAZ-69s or a single T-62. Towards the bow of the craft were two RPDs.
The Yak 31 became the primary Soviet transport helicopter from 1964 to 1991. It saw service heavily during the first Sino-Soviet war, and gained a reputation for reliability. Outside of the Union, the Polish and some other ex-Warsaw Pact nations utilized variants of the Yak 31, though much less extensively than the USSR.