2000 lbs does the trick for all ships.
It's not surprising that dive bombing 'by the book' is pretty hard, when
ALL the acks from 6 Warships are firing at one plane
.. So, when you do a dive bombing 'by the book' - 12000 ft. alt, dive down, drop at 3000 ft. - the odds of survivng are quite low.
Try dropping it from a bit higher than historical alts.. climb to 15k, dive and drop at 5k.
Contrary to popular belief, a drop is a drop regardless of if you die or not. Even if you are killed before the bombs you dropped reach the target, if it is on its mark, the ship will sink. Many times I have receivedf a 'ship destroyed' message 2~3 secs. after I have died and returned to my field, upping in a new aircraft