Because of an accelerated design process the timelines of Merlin development overlapped; for example, the two-stage supercharger was being designed before there was a need to introduce the modified Merlin 45M and 55Ms to counteract the threat of the Focke-Wulf Fw 190.
På grund af en accelereret designproces overlappede tidslinjerne for Merlins udvikling hinanden; for eksempel blev to-trins kompressoren designet før der var brug for at introducere de modificerede typer 45M og 55M for at imødegå truslen fra Focke-Wulf Fw 190.