The Reason Why P-38s Didn’t Have Merlin Engines

Since the P-38 and the P-51 initially had Allison engines, some thought the US missed an opportunity to change the P-38’s Allison engine to a Merlin.

This was due to how much the Merlin engine benefited the P-51 Mustang after the engine change.

Why Wasn’t It Done?

The P-38’s Allison engine already has a two-stage supercharging system, with the additional stage being a turbocharger.

In comparison, the earlier P-51A variant was limited to a single-stage supercharging system so it benefited from the newer Merlin’s two-stage, two-speed supercharger.

Designed For The Allison Engine

The Lightning was designed to accommodate its huge supercharging system. Back when the P-38 was in development, there was no available two-stage mechanical supercharger in production.

By the time the Merlin two-stage superchargers were available, the P-38 had already sorted out its problems regarding its own engines.

Mustangs Were Prepared For The Merlin

Contrary to popular belief, the P-51 didn’t stumble into the Merlin engine.

Sometime around 1941, North American Aviation set aside two airframes just in case the two-staged supercharger was finally available for the Mustang.

As for the P-38, its whole design was based on its Allison engine on both sides. Yes, it did have a rocky start but those were fixed after the release of the P-38J.