December 1940
The British increase their order for NA-73 to 620 aircraft. The additional 300 aircraft would be essentially identical to the first 320, but would carry the NAA designation of NA-83.
12/09/40
Letter issued by the BPC officially naming the NA-73 aircraft MUSTANG. These would be designated as the Mustang Mk I.
Letter was received by NAA on 12/12/40
04/07/41
NAA receives contract for 150 P-51s (NA-91) from AAC four months before 1st XP-51 arrives at Wright Field for testing. This was preliminary to the BPC order for Mustang Mk IAs on 06/30/41. The USAAC designation of P-51 was for the cannon equipped Mustang.
06/30/41
BPC Orders 150 Mustang Mk IA (NA-91) with four 20mm Hispano Cannon mounted in the wings. Defense Aid Contract DA-AC-140
January 1942
No 26 Squadron, RAF becomes the first operational squadron to receive Mustangs. Most of these had a camera mounted behind the pilot's armor for armed reconnaissance with Army Cooperation Command.
01/31/42
In January, 84 NA-73s were accepted by the RAF
04/16/42
USAAF issues contract #AC-27396 for 500 A-36A dive bomber version of P-51. Final contract approval would not come until 08/22/42. (2,5,6)
NAA Model Spec. NA-97 established for production of A-36As.
05/10/42
Operational debut of the Mustang Mk I in combat. The first operation was flown by F/Officer Graham Dawson No. 26 Squadron
5/30/42
1st flight of first of 150 Mustang Mk IAs (P-51) (41-37320) Pilot Bob Chilton (5)
1st tests of A-36 type dive brakes on a Mk I Mustang.
06/08/42
Bob Chilton conducts firing tests of AM190 with 20mm cannon installed in the wings.
06/23/42
NAA Project NA-99 initiated for construction of P-51A Mustangs w/4 .50 Cal wing guns. (5)
AAF Contract #AC-30479 for 1200 P-51A Mustangs with Allison V-1750-81 engine.
July 1942
The USAAF requisition the first 20 P-51s off the assembly lines for tactical reconnaissance. With two K-24 cameras installed, a total of 54 P-51s would be designated P-51-2, but changed to F-6A in October 1942. (5)
AUG 42
First operational use of Mustang Mk.IA aircraft (P-51) by RAF.
08/22/42
Final approval for A-36A contract arrives, while A-36 production already well under way. A/C #'s to 42-83663 through 42-84162. (5)
08/24/42
Final approval for P-51A contract for 1,200 aircraft to be built in 1943. (5)
MAR 43
A-36A Mustangs begin combat operations (2)