The prototype was completed in July and was first flown on 27 July 1947 . Two aircraft were shown at the Tushino Aviation Day Display on 3 August 1947 . It completed its manufacturer 's trials in September and underwent the State acceptance trials from 4 October 1947 to 27 February 1948 where it was redesignated as the Tu @-@ 12 . The NII VVS ( Naoochno @-@ Issledovatel 'skiy Institoot Voyenno @-@ Vozdooshnykh Seel – Air Force Scientific Test Institute ) report summarized the differences between the Tu @-@ 2 and Tu @-@ 12 as " a considerable gain in speed , an improved rate of climb , a higher service ceiling , but poorer field performance and a considerably greater fuel load required to achieve the same range as the Tu @-@ 2 . " Both the lack of a pressurized cabin that greatly reduced its effectiveness at high altitude and the lack of deicing equipment for the wing and tail leading edges and the cockpit glazing were noted as major problems . At high speeds it was virtually impossible to traverse and elevate the manually operated VUB @-@ 68 and Lu @-@ 68 gun turrets . The vibration of the NS @-@ 23 cannon when firing rendered the equipment in the navigator 's cabin unusable and damaged the cabin glazing . Turning on the Identification friend or foe ( IFF ) system adversely affected the intercom system and the radios . New generators had to be installed as the originals did not produce enough electrical power .