Bermuda sits just inside the southern perimeter of a circular barrier reef (the rim of the caldera of a submarine volcano).

Passing St. David's, vessels can either enter into St. George's Harbour, or continue Northward, rounding the East end of St. George's Island, following through another channel that leads to the West, into the waters of the lagoon, from where they can reach the Great Sound, Hamilton Harbour, the Royal Naval Dockyard, and Murray's Anchorage.

Following US independence, the Royal Navy had built up a large naval base in Bermuda, including the dockyard, an Admiralty House, and various subsidiary facilities.

[4] Protecting this base was the primary reason for the British Army's large garrison in Bermuda, with its numerous forts and batteries.

Of all of these, St. David's Head occupied the most decisive position, watching over the bottle-neck through which any force large enough to conceivably seize the archipelago would have to travel (although smaller vessels might pick through the reefs to land raiding parties or saboteurs elsewhere).

An officer of the Royal Navy Examination Service was taken out to meet ships arriving off Bermuda, along with the pilot who would steer the vessel through the reef.

In that position, the naval officer had the task of examining the vessel and its documents before it was allowed to proceed inwards to the lagoon, or any of the harbours.

The British competitor for the 1914 America's Cup, Shamrock IV, was crossing the Atlantic with the steam yacht Erin, destined for Bermuda, when Britain declared war on Germany on 5 August 1914.

Finding all of the buoys and other navigational aids missing, they attempted to pick their own way in through the Narrows, the channel that threads through the barrier reef.

As the firing was to commence at 7am (on 21 January), and it was thought unlikely any vessels would be in the danger area, it was decided to proceed with the salute, ensuring the guns were elevated for maximum range (8,000 yards), out to sea.

[2] The guns were emplaced so that they were difficult, at any great distance, to discern from the slope which fell gently to the top of the cliffs before them.

Beneath the guns were extensive magazines, which fed ammunition up to the firing parties by conveyor belt-like lifts.

Behind these, on Skinner's Hill, was the Fire Commanders Post, which gave orders for gun-laying, the Position Finder Cell and Marine Signals.

As a result, the last regular soldiers (a company of the Duke of Cornwall's Light Infantry) were to be withdrawn in 1957, and the last coastal artillery, the two 6 inch guns of St. David's Battery, removed from use immediately.