During the Napoleonic Wars the route around the north of Scotland via Orkney became important for trade with Scandinavia and the Baltic states because of the danger from French ships in the English Channel and North Sea. However, the northern route was still under threat, both from the French and from US privateers following the US declaration of war on Britain.
By 1813 the US threat had grown to the point that the Admiralty wanted to provide a defended haven in Orkney in which shipping could shelter. Longhope Sound, at the south end of Hoy was chosen. The main defences comprised a battery of eight 24-pounder guns at Hackness with their associated barracks.
In 1814 the defences were improved by the addition of two Martello Towers. One was 200 yards south east of the battery at Hackness, the other on the opposite side of the entrance to Longhope Sound at Crockness. Each carried a 24-pounder gun on the roof. From 1803 over 100 Martello Towers were built in England, but only three in Scotland.
The Longhope defences were upgraded in 1866 in the face of another French invasion scare, and the guns in the battery and Martello Towers were replaced by much larger 68-pounders. Each gun could fire a 68 pound shot a little over a mile, enough to seriously damage any ship of the day. The guns were used once only, for a day's drill by the Orkney Volunteer Artillery in 1892, before being removed in 1900.
The site at Hackness was used by the Royal Navy during WWI, though not for guns, which were instead positioned to defend Scapa Flow more widely. The site at Hackness was sold off in 1922 and converted into a farm. Historic Scotland purchased the Hackness Martello Tower and Battery in 1995 and has since restored both.
Most of what is on view today at the battery dates back to the 1866 refurbishment. The barracks and gun emplacements remain much as they were then (albeit without the guns). The original magazine was removed in WWI, and the officers quarters on view today were modified and extended while in use as a farmhouse from 1922 to 1995.
Hackness Martello Tower has been restored as it would have been after the 1866 upgrade. It is oval in shape and on the side facing the sea the wall is over 4.25m thick. Entrance is at first floor level via a steel ladder. This takes you into the domed barrack room where the gun crew lived.
The room is partitioned to give a separate area for the Sergeant commanding the tower. On the ground floor, accessible only via an internal stair set in the thickness of the wall from the first floor, are the stores and the magazine, plus a tank designed to make the tower self-sufficient in water.
The business end of the tower is the gun emplacement on the roof. The iron tracks used to rotate the gun are original fittings, though the gun fitted to the roof today is a 64-pounder Armstrong gun recovered during renovation of the Caledonian Canal. This is slightly smaller than the guns fitted in 1866, but gives an idea of how the tower would have operated.