Complex sentence: B-29 production started with the − 23 which were all modified to the "war engine" − 23A: other versions were − 41 (B-29A), − 57, − 59.
Split into simpler sentences: B-29 production started with the − 23, which were all modified to the "war engine" − 23A. Other versions were − 41 (B-29A), − 57, − 59.