More than 50 years after a 7,600lb (3,500kg) nuclear bomb was dropped in US waters following a mid-air military collision, the question of whether the missing weapon still poses a threat remains.

Immediately after the crash, a search was set up to find the unexploded nuclear weapon, buried somewhere too close for comfort to the US's second-largest seaport and one of its most beautiful cities.

Numerous other searches have followed, both official and unofficial, and each of them has also proved unsuccessful.

So the bomb remains tucked away on the sea-bed, in an area which is frequently dredged by shrimp fishermen, any one of whom could suddenly find that they have netted something a touch larger and scarier than a crustacean.