The photos appear to be from two different albums.
The first two are of a gun in British service so it may well be rebarrelled to 7.2 in. The other photos (with the spare tyres) may be early US before the M1 helmet was adopted (note the webbing and packs) and if so would definitely be 155mm.
The spare tyres indicate that the tractor used different sized tyres than the gun (or was tracked). the limber and tow bar appear to be the early model which ties into my beleif that this is a US gun early in the war.
Ubique! Mike
