Who used the early Mustangs more?. I'm no expert in this area, but it seems the Commonwealth air forces (mostly the RAF) used the Mustang Mark I's, II's and III's for more roles than the USAAF. groups.
Several photos below credited to: Richard Miller via NAA

P-51 Mustang Mk I, AG346, the first production aircraft to be supplied to the Royal Air Force, on the ground in the USA, July 1941.

Mustang Mk I AG348 Inglewood.

The first production P-51 Mustang (serial number AG 345) painted in RAF Markings and used as a prototype.

RAF P-51 Mustang (serial number AG 349) with a P-40 Warhawk, A-20 Bostons and an A-28 Hudson.

Mustang Mk I 1941.


Allison V-1710 Aircraft Engine correct?


Mustang Mark III, FX889, fitted with a 'Malcolm hood' at Boscombe Down, Wiltshire, following service with No. 122 Squadron RAF.

Mustang IA that was used by Malcolm's for the design, development and prototyping of the 'bubble' hood for the early Mustangs.

Malcolm Hood bulged out to the sides here is a head on view of it fitted to a Mustang I by RAF.

Instrument fitters install a Type F.24 (14-inch lens) aerial camera into the port oblique position in a North American Mustang Mark IA of No. 35 (Reconnaissance) Wing at Gatwick, Sussex, England.

Malcolm Hood Armourers of No 122 Squadron RAF hoist a 1,000-lb bomb into position on a North American Mustang Mark III.

Mustang Mk.I AM106 at Boscombe Down. AM106 was one of several Mustang’s that was allocated for stores testing and trialed zero length rocket launchers, drop tanks and ultimately two 40mm gun pods. AM106 conducted flying and firing trials with the 40mm Vickers, but this weapon was never adopted by the RAF Mustang Squadrons.


Mustang Mk II FR901 with the streamlined external fuel tanks underwing



Armament mods the RAF did to the Mustang I

P-51 Mustang (serial number AG357G) fitted with an experimental rocket installation.
25lb Mk.I type, which was basically a 25lb artillery shell modified to fit as a solid AP shell for the RP-3 rocket motor.

British markings being applied to an RAF Mustang Mk. I at North American Aviation plant in Los Angeles.
At the request of the RAF, North American redesigned the Mustang to be armed with four 20mm in place of the original armament of .30 and .50 caliber machine guns.


Mustang I serial number AM106 sometime during May to June 1943 with Vickers 40 mm "S" cannons.

North American Mustang Mk I of the Air Fighting Development Unit at Duxford, Cambridgeshire, February 1942. Mustang Mark I, AG365, of the Air Fighting Development Unit, on the ground at Duxford, Cambridge. This aircraft subsequently saw much operational.

Mustang Mk I AG422 the aircraft Ronnie Harker, a Rolls-Royce service liaison pilot, flew April 30th, 1942. Resulting in the testing of the Rolle-Royce Merlin in the Mustang.