Complex sentence: Most of the space however, had a height of just three feet between the roof and the covering of transmission and suspension: if the mechanic wanted to assist the right machine gun he had to lay on his belly to load it.
Split into simpler sentences: Most of the space however, had a height of just three feet between the roof and the covering of transmission and suspension. If the mechanic wanted to assist the right machine gun, he had to lay on his belly to load it.