In 1943, the model of Liberator considered by many the "definitive" version was introduced. The B-24H was longer, had a powered gun turret in the upper nose to reduce vulnerability to head-on attack, and was fitted with an improved bomb sight (behind a simpler, three-panel glazed lower nose), autopilot, and fuel transfer system. Consolidated, Douglas and Ford all manufactured the B-24H, while North American made the slightly different B-24G. All five plants switched over to the almost identical B-24J in August 1943. The later B-24L and B-24M were lighter-weight versions and differed mainly in defensive armament.