Flying Fortresses and Liberators, among others, were pretty heavily armed to take on enemy fighter planes. Having about 10 or so barrels lobbing out .50 rounds in all directions seems insane and fearsome, but American airmen suffered some pretty dang high casualty rates. Just how well could they hold up on lengthy missions?
Also, I am linking a piece of film shot and narrated by actor, Clark Gable (who I just discovered served in WW2), that shows a bombing run in action. Just thought it may be interesting to some, as it has some pretty amazing footage of bombers getting attacked.
43:39 is a good place to start.
Thank you for your attention!
I [answered a similar question about a month ago] (https://www.reddit.com/r/AskHistorians/comments/4l8z7d/how_effective_were_the_defensive_weapons_on_wwii/), hopefully there's enough detail there but if you have any follow-up questions do shout.