History of Russian Aircrafts (6)

4k Polikarpov U-2 (Po-2) 1928
6k Kalinin K-5 1929
10k Tupolev TB-3 (ANT-6) 1930
12k Putilov Stal-2 1931
16k MBR-2 hydroplane 1932,
20k I-16 fighter plane, 1934.