Complex sentence: By this time, the VVKJ had lost over 60 per cent of its aircraft; 70 aircraft from the remnants of various bomber and fighter units were assembled for the attack.
Split into simpler sentences: By this time, the VVKJ had lost over 60 per cent of its aircraft. Thus, a total of 70 aircraft from the remnants of various bomber and fighter units were assembled for the attack.