Presumably the door to the aperture for the oblique camera.

The hydraulic system was spewing fluid where the tubing that conveyed it was shot full of holes. The gas tanks were leaking. Nothing worked. The wheels, folded up into the bomber, could not be brought down without its hydraulic system and a belly landing was inevitable.

Well, the undercarriage on a B17 is electric and it can be cranked down by hand. Lowering the gear by hand may not have been possible in the time remaining or the lack of engine power together with airframe damage may have made it seem better to go with a wheels up landing.

The only hydraulics on a B17, ISTR, are the brakes, cowl flaps and windscreen wipers.

Depends where you live! Some forces are relatively happy with artillery.

They must be more common than I realised!

Wasn’t there a Crusader anti-aircraft tank with two 20mm cannon in a new turret?

There was indeed, I was referring to gun tanks! Even less likely as a source though……

The engine in the Beetle looks like a W-670 to me, more like 250 hp.

Any idea what the last pic is of?

Marconi Marksman twin 35mm Oerlikon turret on a Chieftain hull.

One of my Meteors has thrown a couple of rods, presumably from being over speeded. That has three holes in the crankcase, one of which extends into the cylinder block, taking out a section of liner. This sort of damage leads to loss of coolant as well as oil. I suspect the engine still ran but not for very long!