In 1938, Vakhmistrov devised Zveno-SPB (SPB: Sostavnoi Pikiruyuschiy Bombardirovschik, Combined Dive Bomber) which consisted of a Tupolev TB-3-4AM-34FRN mothership and two Polikarpov I-16 Type 5 fighters. Each of the fighters was armed with a pair of 250 kg (550 lb) FAB-250 high-explosive bombs. Although an I-16 Type 5 could get airborne on its own with no more than 100 kg (220 lb) of bombs, once hoisted in the air by the TB-3 it could reach 410 km/h (220 knots, 255 mph) at 2500 m (8,200 ft), had a service ceiling of 6800 m (22,310 ft), and could dive at up to 650 km/h (350 knots, 405 mph). Once the bombs were dropped, the SPB-launched I-16s performed like conventional Type 5s. The three-aircraft Zveno-SPB had a total takeoff weight of 22000 kg (48,500 lb), a top speed of 268 km/h (145 knots, 165 mph), and a range of 2500 km (1,350 NM, 1,550 mi). The use of a mothership increased the range of the I-16s by 80%.