An air burst close enough to the water will cause what is called 'base surge' which, if you are on the receiving end of it, is like a tsunami. That's one reason for detonating the early weapons INSIDE an atoll.
According to the press we stopped carting NDBs (Nuclear Depth Bombs) around in HM Ships as part of the 'Peace Dividend'. They were for dropping on submarines, or rather where a submarine, give or take errors in establishing its position, was likely to be. Possibly an H&S risk for the delivery helicopter. WOOMFAH! & bye-bye Ivan.
WE.177A weighed 272 kg (600 lb), and had a variable yield of 10 kt or 0.5 kt. It was known to the Armed Services as "Bomb, Aircraft, HE 600lb MC". "MC" (Medium Capacity) referred to a nuclear weapon in the kiloton range. The suffix HC (High Capacity) referred to a weapon in the megaton range, although there were some anomalies.
The 0.5 kt yield was used only in the NDB role for detonation above 130 ft (40 m) in shallow coastal waters or in oceanic deep waters to limit damage to nearby shipping. The full 10 kt yield was used below 130 ft (40 m) in deep oceanic waters where no shipping was at risk. The full 10 kt yield was also used by fixed wing aircraft for surface attack. It had air burst, ground burst or laydown options.
Although this variant matched the original Improved Kiloton Weapon concept with an added NDB function, and was identified as the A model, it was not the first to be deployed due to the more pressing needs for the B models. Forty-three were deployed aboard Royal Navy surface vessels of frigate size and larger for use by embarked helicopters as an anti-submarine NDB starting in 1966. When the Navy's large aircraft carriers were decommissioned, twenty warheads were transferred to the RAF. The remaining weapons that were assigned to the Navy's helicopters were retired in 1992.