The ORB has some gems such as:

11th June 1941
2nd Lt Muckley and 2nd Lt Irwin (US Army Corps) attached from No.53 OTU Heston for Operational Training.

So just like Coastal with the USN, Training Command had serving armed forces members of a neutral country undergoing operational training months before Pearl Harbor.

On the 26th June they were posted to RAF Hornchurch.

So the rank and airman may be US Army Corps rather than the suggested Norwegian.

No.53 OTU ORB has a similar notation on 17 May 1941 saying that General Harman and Colonel Cummings US Air Attaches visited the unit to see the US Officers under training.

26 May 1941 No.4 Course reported consisting of 4 United States Army Officers, 4 Officers and 27 Sergeants.