following year. From the late 1950s, the M-4 fleet was converted to the tanker configuration through the fit of a hose-drum unit (HDU) and fuel tanks in the bomb bay and removal of all defensive armament. Similar conversions were performed to the 3M fleet in the 1970s and 1980s, the 3MS-1 "Bison-B" becoming the "3MS-2" tanker and the 3MN-1 becoming the "3MN-2" tanker. Operational history The M-4 was first displayed to the public in Red Square, on May Day, 1954. The aircraft was a surprise to the United States, which had not known that the Soviets had built a jet bomber. However, it soon became clear that the bomber had an insufficient range to attack the United States and still return to the Soviet Union. Only a few of the original production M-4s were actually put into service. To remedy this problem, the Myasishchev design bureau introduced the 3M, known to the West as the 'Bison-B', which was considerably more powerful than the previous version. This new model first flew in 1955. Among other things, two of the five original gun barbettes were removed to lighten the aircraft. In July 1955 American observers saw 28 Bisons in two groups during a Soviet air show. The United States government believed that the bomber was in mass production, and the Central Intelligence Agency estimated that 800 would be available by 1960. The display was a hoax; the first group of ten repeated the flyby with eight more. The classified estimates led, however, to American politicians warning of a "bomber gap". This time, it was not the Soviet Air Force (VVS) that wanted the 3M, but rather Naval Aviation (AV-MF). Though it could still not bomb Washington, D.C., the 3M had a sufficient range to fulfill the need for a long-range maritime patrol aircraft. In 1959, the 3M broke numerous world records for payload to height, including to and to . However, it was thought by the West (and would continue to be thought until 1961) that the 3M was the original M-4, meaning that the capability of the M-4 was vastly overestimated by Western intelligence agencies. In the early 1960s, the 'Bison-C', with a specialized search radar, was introduced. By this time, many of the original M-4s had been converted to M-4-2 fuel tankers for aerial refueling. Later, 3Ms were converted to 3MS-2 and 3MN-2 tankers as well. Neither the M-4 nor