There will be a message in the text buffer if you destroyed an object (or killed another player)
You can also hit F3, then F8. Then you can freely move your external view around with the numberpad keys, for example to look down to see explosions.
Of course, in bombers like the B-24 you can simply jump to your belly gunner position.
More info about level bombing:
http://trainers.hitechcreations.com/ Chapter "Level Bombing Techniques"