Further attempts were made to upgrade the firepower of the aircraft using 20 mm (0.79 in) ShVAK cannons, making the I-16 one of the most heavily armed fighters of the period, able to fire 28 rounds of ammunition in three seconds. Pilots loved the results, but the cannons were in short supply, and only a small number of the I-16 Type 12, 17, 27, and 28 were built. The cannons adversely affected performance, with 360° turn time increasing from fifteen seconds in the Type 5 to eighteen seconds. The Type 24 replaced the skid with a tailwheel and featured the much more powerful 670 kW (900 hp) Shvetsov M-63 engine. The Type 29 replaced two of the ShKAS guns with a single 12.7 mm (.50 in) UBS. Ten Type 17 fighters were supplied to the Chinese Air Force where on 20 May 1940, they effectively shot down a C5M scout-attack plane and three G3M bombers during the Battle of Chonqing.