Bigger WWII bombers like e.g. the B-17 Flying Fortress were equipped with lots of machine guns for self-defense against single-seat fighter aircraft.
Defensive armament increased from four 0.50 in (12.7 mm) machine guns and one 0.30 in (7.62 mm) nose machine gun in the B-17C, to thirteen 0.50 in (12.7 mm) machine guns in the B-17G. But because the bombers could not maneuver when attacked by fighters, and needed to be flown straight and level during their final bomb run, individual aircraft struggled to fend off a direct attack.
The last sentence and the fact that fighter escort was developed and also personal impression from live footage etc. indicates that the self-defense armament wasn't very effective. Is this true?
I can understand that bombers cannot do evasive maneuvers, but so does the attacking fighter plane when it is homing in on the bomber and aiming, isnt it? In that moment the bomber actually should have the advantage of being able to point the (several) mobile guns, while the fighter must use the entire airframe to aim its guns and thus has a very predictable flight path.
And in case it really wasn't effective, why did they carry it then? Must have added a lot of additional weight.
Are there any figures to illustrate the effectiveness of bomber self defense?