I have no idea about the statistics, but in a wartime scenario this leaves out a crucial factor: number of enemies killed So if you send out 100 B17s with guns

I have no idea about the statistics, but in a wartime scenario this leaves out a crucial factor: number of enemies killed So if you send out 100 B17s with guns and 80 come back, but they kill N enemy attackers, and 100 B17s without guns and 90 come back, but kill 0 enemy attackers, maybe if N is high enough it's worth it?