The Halifax was powered by four engines, two spaced evenly on each wing. Early production Halifax bombers were powered by models of the Rolls-Royce Merlin engine; later aircraft were commonly powered by the larger Bristol Hercules radial engine. To contain and attach the engines to the airframe, Handley Page developed their own design for the power egg instead of using the typical, slimmer Rolls-Royce counterpart; despite generating increased drag, this in-house design was readily adaptable to the alternative Hercules engine on later aircraft.