Excuse the ignorance - what does NBS stand for?
Navigation and Bombing System?
Hmm question answered I think?
http://www.tatjavanvark.nl/tvve/dduck0.html
Gosh - so it could be a fully automated process?
Makes sense I suppose, given the speed you are travelling at - the need for the weapon to fly the correct profile etc.
There must have been a point in programming the system where you were effectively committed to a release.
Perhaps the OP's question shouldn't have been who pushed the button, but who could abort the weapon release!