https://en.wikipedia.org/wiki/Soviet_Union_in_the_Korean_War
https://www.rbth.com/history/332396-how-soviets-fought-against-americans
Throughout the war, Moscow provided Hanoi with 95 S-75 air defense missile systems, over 500 airplanes, 120 helicopters, more than 5,000 anti-aircraft guns and 2,000 tanks. In addition, more than 10,000 Soviet military specialists were dispatched to Vietnam: from missile crews, pilots and signalmen to tank crews and doctors.A special role was also played by Soviet anti-aircraft gunners. They not only trained Vietnamese People’s Army (VPA) personnel, but also took part in fighting themselves. It is in no small degree thanks to them that the U.S. Air Force and Navy, having lost more than 4,000 aircraft, failed to suppress North Vietnam's air defenses and defeat the country.
Rim Kazakov, a guidance systems officer with the 274th Surface-to-Air Missile Regiment of the VPA: “To give credit to our Vietnamese comrades, they successfully mastered the weaponry entrusted to them and were always by our side. In addition to taking part in actual combat with missile crews, we - having learnt some basic Vietnamese - regularly conducted training using simulation equipment. We overcame the psychological barrier of the first launches together: I pushed the ‘Start’ button and the Vietnamese guidance systems officer only pushed it already after the launch, sometimes probably not even suspecting it.”
