Complex sentence: Unfortunately, both types of torpedo bombers suffered heavy casualties, with only one Avenger surviving, although they were credited with drawing away the Japanese combat air patrols so the American dive bombers could successfully hit the Japanese carriers.
Split into simpler sentences: Unfortunately, both types of torpedo bombers suffered heavy casualties. Nonetheless, the US torpedo bombers were credited with drawing away the Japanese combat air patrols so the American dive bombers could successfully hit the Japanese carriers.