That paint scheme was applied to the model 322-B Lightning Is built for the RAF that were rejected and taken over by the USAAF to use as test ships and trainers. No superchargers or handed engines. Armament was 2 .50s and 2 .30s with no cannon.
The one pictured is the first 322-60-04 Lightning II, which was also rejected by the RAF and was reclassified as the P-38F-13-LO after being returned. Some saw combat as regular P-38Fs or Gs, but others, like this one, were retained stateside and used as testbeds by Lockheed and the AAF. That one pictured was stressed to carry 2 2,000 pound torpedoes or 1 torpedo and 1 300-gallon drop tank. The torpedo was successfully test dropped, but the rig was never tested outside the US.