During the final years, RAF Khormaksar had been vulnerable to terrorist mortar and small arms attack; this risk was reduced and very largely held in check by the use of ground forces patrolling possible base plate areas and vantage points to the north of the airfield as well as by frequent day and night Internal Security patrols being flown by helicopters; however, there were in all three mortar attacks on the Station between 1965 and 1967. The last in August of 1967 was successful in so much that three aircraft on the main transport apron sustained minor damage; fortunately only two bombs actually landed on the apron due to poor weapon laying technique. By way of passive defence the Station endeavoured to reduce the effects of any such attacks by maintaining the maximum degree of aircraft dispersal compatible with operational requirements - this in practice resulted in the apron, capable of taking 29 major aircraft, rarely being used to more than half capacity. This was achieved by parking squadron light aircraft in hangars whenever possible where a degree of immunity was assumed against all but a direct hit and by dispersal of maritime and MR transport aircraft to more remote areas such as the wash pan area and the rear of the hangars in the helicopter operating area. There was no doubt that those measures considerably reduced the RAF’s vulnerability to surprise attack and was relatively effective.
However, to achieve a greater degree of protection on the operating apron some form of wall or revetment was required, but the cost, time and materials for building effective conventional revetments had ruled out any projects in this direction. The fuel strike in June 1967 and the need to transport drummed fuel stocks was instrumental in overcoming these difficulties; the Station realised that here was a useful, cheap and readily available building material. Drums were placed in position empty, to ease manhandling, and then filled with water; to use sand would have entailed filling the drums first and at a tediously slow rate which together with the difficulties in transporting, lifting and manoeuvring ruled this out. Liquid concrete would be the ideal filling media, however water was adequate as attacks were not expected to be frequent or sustained.
The arrangement of walls was designed to protect an aircraft’s pressurised fuselage rather than all parts which would have involved the greater difficulty of higher walls with a reduction in stability, safety factors as well as the increased risk to aircraft taxiing and to IT movements. To achieve the same degree of protection, which would have been given by higher walls, a series of smaller parallel walls were used, spaced so that the cut off angle from the base of each wall would give full protection up to the top of the fuselage. Three such walls 6 ft high (two drums) give full cover over the ‘heaten zone’ of 81 mm mortar. The space taken up by the series of walls would anyhow have been left clear because the principle of dispersal had not been abandoned, but the ‘in-use’ dispersals have, however, been given very substantial protection.
Each side of the parking apron itself was additionally protected, on the one hand by existing buildings such as hangars and associated flight line offices, on the other by a special twelve foot high wall of drums. This latter protection also gave cover against small arms fire from the airfield boundary some 500 - 1,000 yards away.
To guard against shrapnel debris in unprotected entrances to the dispersal pans, special trolleys (adapted from bomb trolleys) hitched together to form a ‘train’, were used as the foundation platform of mobile walls built with the same 40 gallon drums - the space between each trolley (i.e. above the towing arms) being filled by a curtain of rubberised horse hair (packing material); the rubberised sheets were suspended from a metal bar capable of swivelling to allow for turns when towing. These mobile walls were positioned by tractors both fore and aft of an aircraft, immediately on arrival on the pan, thus completing a fair measure of all round protection. The wall of drums for each dispersal were spaced 1½ wing-spans apart of the largest aircraft likely to use the dispersal frequently, in this case 215 ft for the Britannia. The same protection principle was extended to helicopter and fighter dispersals but of course these aircraft with their lower profiles were afforded considerably better protection as indicated in the photographs.
It was considered that this easy, quick and cheap method of building hundreds of yards of wall, had much to commend it under similar circumstances; although the protection obtained was limited to a degree, it nevertheless also provided a useful visible deterrent to any would be terrorist as he would have exposed himself by launching a mortar attack, with even less certainty that it would be effective.