Complex sentence: As of 20 December 1945,3,741 American lend-lease ships to the Soviets were 36 which capable of mounting an invasion of Japan but clearly not enough to pose enough threat to Japanese forces in the mainland.
Split into simpler sentences: As of 20 December 1945,3,741 American lend-lease ships were given to the Soviets, 36 of which were capable of mounting an invasion of Japan. This was clearly not enough to pose a large threat to Japanese forces in the mainland.