Complex sentence: The US Navy's TBF Avenger torpedo bombers suffered particularly heavy loses as their low-level attack runs were vulnerable to anti-aircraft fire; as the bombers' torpedoes were also set to run too deep these attacks achieved little.
Split into simpler sentences: The US Navy's TBF Avenger torpedo bombers suffered particularly heavy loses as their low-level attack runs were vulnerable to anti-aircraft fire. As the Avengers' torpedoes were set to run too deep these attacks achieved little.