The interim project was given the OKB designation "77" (ANT-77) but would have the official designation Tu-12. Work began in April 1947 even before an official decision was reached authorizing the Tu-12/"77" project. By May of that year the Soviet Air Force reviewed Tupolev's full-scale mockup. Even before the Air Force review of the mockup, Tupolev ordered work to begin in the OKB's workshops converting standard Tu-2S bombers to the Nene-powered configuration. At the end of the month the Air Force authorized conversion work to begin based on their mockup review.
For the sake of expediency, the changes to the Tu-2 bomber were kept to as few as possible. The main differences between the Tu-12 and the Tu-2 were as follows:
- The Shvetsov ASh-82FN radial engines and nacelles were replaced by longer nacelles housing the Rolls-Royce Nene turbojets.
- The wing dihedral was reduced from 6 degress to 3 degrees.
- The fuselage was stretched with a nose extension allowing the bombardier/navigator to sit ahead of the pilot and a rear fuselage stretch to balance the change in the cockpit. The height of the midfuselage was increased with the top of the pilot's cockpit even with the top of the aft gunner's canopy.
- A tricycle undercarriage was fitted with the mainwheels rotating 90 degrees to lie flat at the bottom of the nacelles.
- Additional fuel tanks were added to compensate for the increased fuel consumption of the jet engines.
- Adjustments were made to the control system to compensate for higher speeds.
- The tail structure was reinforced as well to handle the increase in speeds.
Six Tu-12s were made by converting Tu-2s. One aircraft was used as an engine testbed, another was used as part of jet drone development and the remaining four were used by the Soviet Air Force for crew training and familiarization for aircrews bound for the definitive Tu-14. The experience in developing the systems for the first Soviet jet bomber would serve Tupolev well during the development of the Tu-16 "Badger" and Tu-95 "Bear" bombers.
Source: OKB Tupolev: A History of the Design Bureau and its Aircraft by Yefim Gordon and Vladimir Rigmant. Midland/Ian Allan Publishing, 2006, p117-121.