I've read or heard eyewitness accounts of WW2 bombers exploding or rather nearly vaporizing under fire.
I imagine the main cause would have been flak, 88-mm sized, however it seems that an explosion from an 88 round might blow up a plane, set it alight, etc, but it doesn't seem that size round would 'vaporize' an airplane the size of a bomber.
I wonder if anti-aircraft fire either flak or plane to plane ever ignited the ordinance inside the plane, causing a the massive explosions. For example a direct hit on a 500 or 1000 lb bomb exploding, and in turn setting off the other bombs nearly simultaneously.