Rosyth Dockyard and the Forth were very vulnerable both during WW1 and WW2 and so various defences were constructed around the Forth.  On the coast north of Dirleton and close to the island of Fidra, a Battery was built at the start of WW2 and equipped with guns which were intended for use against any large warships which attempted to enter the Firth of Forth or to shell targets outside the estuary.
This became operational in 1940, having been set up in a considerable hurry. Mr. Tom Porteous, a forestry worker on Archerfield Estate, was far from pleased when he was given a mere twenty-four hours notice by the Army to vacate his cottage to allow the construction of the battery. ……   In an attempt to disguise its real function extensive camouflage measures were employed at Fidra. False sloping roofs were provided, from which canvas curtains were hung, the effect of which was to turn the gun houses into apparently innocent domestic dwellings, and therefore of no interest to German photographic intelligence. 
Just below the battery, a pillbox was built which housed a searchlight to illuminate targets for the gun battery and its remains still stand beside the footpath on the cliff.
 A photo of the disguised battery and the searchlight pill box is here with further details.