the 3M ever saw combat, and none were ever converted for low-altitude attack, as many American B-52s were, nor were any ever exported to the Soviet Union's allies. Production of the Bison aircraft stopped in 1963, by which time 93 of them had been built. The last aircraft, an M-4-2 fuel tanker, was withdrawn from service in 1994. The three VM-T heavy lift aircraft were converted from 3MN-2 tankers, with very large loads carried piggy-back above the fuselage. The single vertical fin/rudder was replaced with two large rectangular fin/rudders at the tips of the horizontal stabilizers to improve control due to the turbulence caused by the cargo pod. With the withdrawal of the Myasishchev bombers and tankers the vast majority of the retired airframes were broken up under the terms of the relevant arms limitation treaty. Variants Izdeliye M (Product M) – the in-house designation for the SDB, Project 25, M-4 aircraft. SDB (Strategichesky Dalny Bombardirovshchik – strategic long-range bomber) – The government designation for the M-4 programme. [Tema Dvadtsat Pyat] Subject 25 – The VVS designation for the strategic bomber program. Myasishchev M-4 – The designation used for production aircraft. 35 built including two prototypes and a static test article. (NATO Air Standards Co-ordinating Committee codename Bison-A) Myasishchev M-4-2 (a.k.a. M-4-II) – M-4 production aircraft converted to in-flight refueling tankers. (NATO Bison-A) Myasishchev 3M – The improved M-4 with Dobrynin VD-7 engines with higher thrust and better S.F.C. than the Mikulin AM-3A engines. The first prototype was converted from an M-4.(NATO Bison-B) Myasishchev 3M-5 – The improved M-4 with Dobrynin VD-7 engines with higher thrust and better S.F.C. than the Mikulin AM-3A engines, configured as a launch platform for the KSR-5 air to surface missile. One prototype aircraft converted from a 3MN-1 bomber, but further conversions not carried out due to the limited life remaining on candidate aircraft. (NATO Bison-B) Myasishchev 3MD – Production cruise missile carrying aircraft for carrying the P-6, KSR or Kh-10 air to surface missiles, with only nine built in 1960 before the production line was shut down and the Myasishchev OKB dissolved. (NATO Bison-C) Myasishchev 3ME – A comprehensive avionics upgrade was tested on the sole 3ME, converted from a production 3M bomber (c/n 8301101). New navigation and radar equipment and a completely revised fire sensing and suppression system were also fitted. The prototype was damaged beyond repair when the Myasishchev M-50 prototype jumped