The P-38 Lightning particular cockpit configuration and space limitations, especially for the first variants, always caused problems when trying to fit gunsights. Only two types of gunsights were used during its career:
- The N-3 series (and ST-1A for the very few P-38 supplied to the RAF) up to the P-38H;
- The Lynn L-3 and its derivatives (LY-3N and G-1) from the P-38J onwards.
The N-3 was mounted in a nearly horizontal position between the windscreen and armoured glass protecting the pilot. Only 2 types of mount and corresponding sightheads, both designed and procured by Lockheed, were used. The first one, quite bulky and obstructive to pilot vision, was later replaced (from P-38G-10-LO if information on factory drawings are correct) by a leaner version where the reflector glass was only held at the bottom.
The P-38J, with its redesigned cockpit, was initially planned to be fitted with the N-9 gunsight. But all trial fittings proved unsatisfactory and Lockheed finally turned to the Lynn company and the L-3 gunsight. This was supposed to be only a temporary measure until the N-10 and/or the Eastman Gunsight would become available (they were never put into production) or the K-14 could be used (which also never happened for the same space limitation issues encountered with the N-9).
I am not aware of any depot or field modification to fit any other gunsight to the P-38 series.
The P-39 was only fitted with one gunsight during its career: the N-2 and N-3 series.
The first models were fitted with an N-2A and corresponding AAF procured sighthead but it was quickly replaced by the N-3 series with a smaller, leaner and better sighthead designed and procured directly by Bell. I’ve also read quite a few period AAF correspondance about A-1 variable sightheads being fitted to P-39; but have so far not been able to find a single period photo of such an installation.
I am not aware of any depot or field modification to fit any other gunsight to the P-39 series.