The Mil V-12 was the largest helicopter ever made. Only 2 were ever produced by the Mil Design Bureau. It's primary role was to be a heavy lifter.
When the Soviet Union needed a gigantic helicopter able to transport massive loads military equipment, who did they call? The Mil Design Bureau of course. In 1965 they got to work on prototype model V-12. In a rather short period of time just about 2 years later on June 27, 1967 the first prototype performed its first lift off-touchdown test. Upon landing the a tire burst, and its wheel disc was bent. Back to the garage. After repairs and alterations it made its first flight on July 10, 1968 from the Mil factory pad in Panki to the Mil OKB test flight facility in Lyubertsy.
The helicopter known as "Homer" by NATO set many records including reaching an altitude of 7,398 ft. It also won the Sikorsky Prize. But after all the testing to get this beast of the ground, and all the money put into building it the Soviet Union canceled production plans. Only 2 prototypes were ever built. Both with the same registration number SSSR-21142. The first one sits at the Mikhail Leontyevich Mil helicopter plant in Panki-Tomilino, Lyuberetsky District near Moscow, and the second one is on display at the Monino Air Force Museum. Its specs are as follows.
Length: 121 ft 4 in,
height: 41 ft,
max speed: 260 kmh,
fuel range: 310 mi,
service ceiling: 11,500 ft.