Complex sentence: As bombers grew and multi-place aircraft became common, it was no longer possible for the pilot and bomb aimer to share the same instrument, so the bomb aimer had to take over the duty of adjusting for drift, relaying commands to the pilot.
Split into simpler sentences: As bombers grew and multi-place aircraft became common, it was no longer possible for the pilot and bomb aimer to share the same instrument. The bomb aimer had to take over the duty of adjusting for drift, relaying commands to the pilot.