Complex sentence: Apart from the aforementioned I-15, I-16 and UT-4, the Soviets also supplied bombers Tupolev TB-3, Tupolev SB, Ilyushin DB-3, over 1,200 aircraft had been sent to China by the end of 1941.
Split into simpler sentences: Apart from the aforementioned I-15, I-16 and UT-4, the Soviets also supplied Tupolev TB-3, Tupolev SB, and Ilyushin DB-3 bombers. Over 1,200 aircraft had been sent to China by the end of 1941.