I agree with Joe.
RAF aircraft of WW2 had 'steady' wing tip lights (Red/Blue [or greenish blue]), with a white light on the tail, and sometimes on the fuselage spine (example Spitfire and Hurricane).These fighters also had an 'amber' light on the underside center section, used as an I.D. or signal lamp, which could be 'steady', or switched to a Morse key to signal 'Letter of the Day'.
Larger (British) RAF aircraft, such as the Lancaster, or Mosquito, had a row of three, hooded lamps on the underside fuselage, similar to the American lay-out, in Red, Amber, Green, which again could be set in combination, or 'flashed' in Morse code. There was a also a 'shielded', dim lamp, buried in a tubular housing on the outer wings (thename of which escapes me!) which could only be viewed from directly behind.
I'm not exactly sure when the 'modern' style of flashing wing tip and tail lights was introduced, but this followed on from the first stage of a rotating, or flashing, strobe light 'anti-collision' beacon, first mounted either on the top of the fin, or the fuselage spine, and then later also added (sometimes, depending on type) to the fuselage underside. I think the 'all flashing' transition was in the late 1960's to early 1970's, but of course, aircraft from earlier periods were/are up-dated to meet the regulations of the period, so, for example, a currently airworthy DC3/C-47, would probably have 'all flashing', as opposed to the original 'fit'.
So basically, for WW2, your P-38 would have 'steady' nav lamps.
Hope this helps.