During January 1941 the R.A.F. authorised work to be
carried out to prepare part of the estates of Colstoun and Lennoxlove
for use as No. 27 Satellite Landing Ground (S.L.G.).
The role of R.A.F. Lennoxlove was as a secret place for the storage of replacement aircraft, where the enemy would be unaware of their presence and the aircraft would therefore be safe from attack. The landing ground was to be part of No. 18 Maintenance Unit (M.U.) which was based at R.A.F. Dumfries.
Work extended from January to April, with permission being gained from the 'Chief Constable' at Haddington to close by means of self-shutting gates at each end, a small road running across the landing strip. Finally, on 24 April 1941 a Fairey Battle light bomber made a trial landing at Lennoxlove which proved successful and the landing ground was declared acceptable.
On 25 April a Bristol Blenheim was flown in, the first aircraft to be stored at No. 27 S.L.G. However, despite this achievement it was decided that only smaller aircraft, such as Hurricanes, could be stored at Lennoxlove because the landing strip had not been extended, this being due to delays in getting planning permission to close the road separating the extension from the rest of the landing ground. However, some progress was made, and by the end of May 1941 all flight equipment huts were complete and a telephone line had been installed at the headquarters office. Additionally, an Army guard of one officer, two N.C.O.s and 12 men of the 10th Royal Scots was billeted in Lennoxlove House.
Permission to close the road necessary to extend the landing strip was not slow in being given by Haddington Police and once the work was completed, which included lowering the surface level of the road to avoid it sitting proud of the grass runway, many more Blenheims were flown in to Lennoxlove.
The Commanding Officer of No. 18 M.U. visited Lennoxlove in August 1941 and gave some thought to the possibility of landing Westland Whirlwind twin-engined fighters there. The unit's Chief Test Pilot mentioned that the Whirlwind swung badly in crosswinds but was nonetheless prepared to attempt a landing when the wind conditions were considered suitable. This was carried out very successfully and, as a result, many Whirlwinds came to be stored at Lennoxlove. Even larger aircraft were to be flown in to the S.L.G., with Vickers Wellington bombers making their first appearance in late 1941, and even a Handley-Page Halifax four-engined heavy bomber landing here in the summer of 1942, the S.L.G. being declared ideal for such large aircraft.
By November 1944 No. 27 S.L.G had 119 aircraft in storage, most of which were Wellingtons. Quite a number of these suffered damage as a result of branches falling from the trees under which they were hidden, and even from trees themselves, uprooted during gales.
In the summer of 1945 Lennoxlove gained a unique distinction. A derivative of the Whirlwind fighter was the Westland Welkin which was designed as a high-altitude day and night fighter, intended for intercepting German bombers flying at great heights. This threat did not materialise and thus the Welkin never saw operational service. However, 67 Welkins were produced (as well as two prototypes), most of these being flown into Lennoxlove for storage at the end of the war, before being scrapped.
The end of No. 27 S.L.G. followed not long afterwards, beginning in August 1945 and ending with the closure of the unit the following month.