Perhaps one of the most significant advances in warfare during the twentieth century was the development of air power. Although very much in its infancy at the time of the First World War, by the outbreak of the second, military aviation had advanced to the extent that it played a decisive role in the conflict.
During the interwar period, theories abounded concerning the future nature of war based on the experiences of WWI. As the newest weapon to the battlefield, much was written about the potential of air power. In 1921 the Italian General Giulio Douhet had perhaps the greatest influence on military strategy in the late twenties and early thirties with his publication ‘Command of the Air’.
In this paper he developed the concept that the bomber would always get through arguing that bomb laden aircraft would be able to fight their way to and from a target and that control of the air could win a war regardless of land or sea power.
It is not surprising that this school of thought had a major influence on defence construction. Air protection became a far more serious consideration for military installations across the British Empire than it had been in WWI. This situation is particularly well illustrated in Orkney where anti-aircraft (AA) defences were built and men recruited to man them in January 1938, well in advance of the other defences.
Anti-aircraft batteries were initially constructed to provide defence for strategic military complexes that were viewed as being potential bombing targets. In 1938 the sole land-based site that matched these criteria in Orkney was the fuel oil depot at Lyness on Hoy which served the British Fleet.
The defences consisted of two half batteries of anti-aircraft guns located on the raised ground to the immediate north and south of the depot. These positions were manned by Orcadian men of the recently formed 266 Heavy Anti-Aircraft Battery equipped with four 4.5 inch anti-aircraft guns each.
AA gun defences can be loosely divided into two categories, Heavy anti-aircraft (HAA) and Light Anti-aircraft (LAA). The HAA sites were largely permanent consisting of four guns mounted in the centre of their own circular earthen embankment each of which had concrete lockers for storing ammunition.
These four emplacements were evenly positioned in a semi-circular ‘C’ shape around a central battery command post with the bulge of the ‘C’ pointing roughly in the opposite direction to the area being defended so as to cover the approach to the target.
The command post housed a spotter’s telescope, rangefinder and predictor computer. This equipment was used to calculate the distance, speed and height of approaching hostile aircraft. This information was then passed to the guns where it would be used to set the fuses on the projectiles and tell the gunner where to aim.
The 4.5 inch and later 3.7 inch guns that HAA batteries were equipped with were used to engage high altitude bombers and fired high explosive projectiles designed to explode underneath or above a bomber, causing damage as hundreds of hot metal fragments flew through the air around it.
As the military presence in Orkney grew so too did the defences. Twenty six HAA batteries in total including some mobile gun units were emplaced in Orkney during WWII and formed a defensive ring around Scapa Flow. As technological advances were made, HAA sites began to be equipped with gun-laying radar as a means of detecting hostile aircraft and directing the guns.
(c) Gavin Lindsay