Operation Swordfish in 1962 saw a 10-20 kT nuclear depth bomb tipped ASROC detonated 198 meters underwater less than 4000 meters from the ship that launched the weapon. The weapon exploded 40 seconds after impacting the water, the resulting spray dome was 3000 ft across and reached a max height of 2100 feet around 16 seconds after detonation. If the helicopter dropping the weapon was already moving at the drop point, it would have very likely outrun any weapons effects that broke the surface.