A total of 250,000 tons of German chemical weapons had been discovered, the majority of which were destroyed because they comprised warfare agents which the allies already possessed in great abundance e.g. mustard gas at sites such as RAF Bowes Moor.
As a result, captured stocks of German nerve agents were divided between Britain and the United States after discussion, with the Americans taking the sarin.
The British transferred their 14,000 tons of ordnance containing tabun in October 1945, via Hamburg and Newport, to temporary storage at the RAF strategic reserve ammunition store at Llanberis.
Finally in June 1954 it was decided to dispose of the entire stock because by then it was recognised that not only did the weapons have no military value but they had actually become a liability, which could only become worse as time passed.
Operation Sandcastle was divided into two sections, a sea voyage to Cairnryan and then a transfer to suitable hulks there for later sinking north-west of Ireland beyond the continental shelf.
The work began with the construction of a road between Llandwrog and the nearby port of Fort Belan where six tank landing craft were assembled.
They reached the scuttling point (56°30′00″N 12°00′00″W / 56.50000°N 12.00000°W / 56.50000; -12.00000) in the early morning of 27 July, but waited until 10:00am for the arrival of an RAF photo-reconnaissance aircraft to observe the operation.