Landships II

I enclose a photo that I've designated Whippet P2. It appears in a number of books and is said to be the prototype Medium A after the fuel tank has been moved to the front and the turret removed and superstructure raised but before the circular gun ports have been fitted. At first sight this makes perfect sense as the fuel tank lacks its armoured cover and there are five mud chutes rather than the four on the production Medium B. However if we look at the photo of the prototype before the fuel tank was moved see photo I've designated Whippet P1. (This photo also appears in David Fletcher's Landships albeit much darker). This has the fuel tank at the rear and the engine compartment side has not been pierced for the air ontakes necessary when the fuel tak is at the front blocking the original air intake. The superstructure has been built up - and is fitted with the circular gun ports! So the earlier photo of the prototype has gun ports fitted but the 'later' one is waiting for them to be fitted. My question is were there two prototypes or did the Whippet always have a circular gun port on the Starboard side anyway?