Allied fighters used head-on attacks to attempt to scatter formations of Luftwagge medium bombers, then they would pick off the stragglers.
German fighters used this type of attack against the heavily gunned Allied bomber formations, since they have the least amount of firepower toward the front.

The trick is to attack at a zero deflectioon angle, flying straight at the bombers. Wait until the last possible second to fire and pull up. Gutsy fliers will fly trough the formation. A more conservative approach is to break downward and away from the bombers' defensive fire.

Drawbacks:
The high rate of closure can lead to mid-air collisions.
Even with the biggest bombers, the small deflection angle means a verysmall chance of hitting any vital areas. A good target on a bomber is the cockpit, but it can be hard to hit when the rate of closure is so high.