Airborne units of two divisions (7th and 31st Guards) were used during Soviet operations in Hungary during 1956, and the 7th Guards division was used again during the 1968 invasion of Czechoslovakia. The first experimental air assault brigade – the 1st Airborne Brigade – was apparently activated in 1967/1968 from parts of the 51st Guards Parachute Landing Regiment (PDP) (Tula), after the Soviets had been impressed by the American experiences in Vietnam. In 1973 the 13th and 99th Airborne Divisions were reorganised as air assault brigades, and thus the number of divisions dropped to eight. There were also independent regiments and battalions. However, even by the 1980s only two divisions were capable of being deployed for combat operations in the first wave against NATO using Air Force Military Transport Aviation and Aeroflot aircraft.