[Francis McClobber]

The rate of closure of the smaller aircraft would indicate it needed to either an underrun or overrun due to an excessive rate of closure.

When conducting such a maneuver, the plane closing needs to either gain or lose altitude. (underrun is safer because the closing pilot can see the other aircraft at all times)

Judging by his bank angle, he most likely lost sight of the B-17 due to his bank angle.

[GingisK]

I honestly can't tell if it was a P-51 or a Spitfire. The Spitfire is really blind to the underside due the placement of the cockpit relative to the leading edge of the wing. I'm pretty sure the P-51 has pretty good visibility in the region of that approach.

The shape of the fighter's wing looks like maybe a Spitfire rather than a P-51. Difficult to tell.

And there you have it, WWII fighter planes are as blurry as UFOs, even with modern video gear.

[GingisK]

Hey, FM, the fighter was a Bell P-63. That looks like it should have really a good forward view, even downward. The nose is very slender ant the pilot is way ahead of the leading edge.