if the cap's screw thread got just a little bit corroded maybe it would stick and not unscrew itself?
I am sure that the armourers would be most offended at that suggestion. No doubt the cap would periodically be removed and greased.
Navigator would fuse the D/C's remotely from within the aircraft, the D/C's being hung under the wing?
The Depth charges, and any other stores would be attached to Electromagnetic release units, whether in a bomb bay or on a wing. These would be released electrically from the pilots or Navs bomb firing switch. Similarly, the fusing unit was electrically operated. The jaws were spring loaded open, (which meant the safety wire would stay with the D/C,) and were closed electrically to retain the wire so that the D/C would drop live.
On the run up to a drop, the Nav would call "weapons selected and fused" Weapons selected meant that he had made connections between the chosen weapons and the bomb firing switch. Fused meant that he had closed the jaws of the fusing units so that they would drop live.
Some time ago I came across a video on the net of D/Cs being loaded onto a Sunderland. I cannot now find it - if someone does perhaps they could add it to this thread.