Beaufort's Dyke is a deep sea trench between Northern Ireland and Galloway within the North Channel that separates Ulster from Great Britain. The trench is thirty miles long, two miles wide and 650 feet to 1,000 feet deep.
The feature is named after Francis Beaufort, Hydrographer of the Navy, who revolutionised hydrographical surveys and discovered the feature.
- Location map:54°47’6"N, 5°25’12"W
Because of the depth of the dyke and its convenient proximity to the Cairnryan military port, Beaufort's Dyke became the United Kingdom's largest offshore dump site for conventional and chemical munitions after the Second World War; in July 1945, 14,500 tons of 5-inch artillery rockets filled with phosgene were dumped in Beaufort's Dyke.
The Ministry of Defence estimates that there are well over a million tons of munitions at the bottom of Beaufort's Dyke 
Munitions have subsequently been washed up on beaches in the area. In particular, in 1995, incendiary devices were discovered on the coasts on either side of the North Channel. This coincided with the laying of the Scotland-Northern Ireland pipeline (SNIP), a 24-inch gas interconnector being constructed by British Gas.
According to documents discovered at the Public Record Office, approximately two tons of concrete-encased metal drums, filled with radioactive laboratory rubbish and luminous paint, were dumped into Beaufort Dyke, a thousand feet deep and six miles off the Scottish coast.
Projects for a tunnel, a causeway or a bridge between Ulster and Scotland have been suggested at various times from the late nineteenth century onwards. The Dyke has always been an important problem for such proposals, in terms of both practicality and cost: any tunnel would have to delve a thousand feet deep and into geologically unstable rock, and bridge pillars could be placed so deep.
- Parliamentary Debates, House of Commons, 23 April 2002 , columns 192W–193W, (Dr Lewis Moonie]], Member for Kirkcaldy]]).
- 'UK's undersea 'ticking timebombs'' – Alex Kirby in BBC New Science and Technology, 6 November, 2004
- Arthur, Charles (1 July 1997). "Ministers admit nuclear waste was dumped in sea". The Independent (London: Independent News & Media). https://www.independent.co.uk/news/ministers-admit-nuclear-waste-was-dumped-in-sea-1248343.html. Retrieved 29 April 2015.
- Kinaham, G.H.: Beaufort's Dyke off the Coast of the Mull of Galloway: Proceedings of the Royal Irish Academy (1889-1901), Vol. 6 (1900 - 1902), pp. 26-32, 828
- 'What lies beneath?' – The Galloway Gazette 25 March 2005
- G Ford, L Ottemöller, B Baptie: 'Analysis of Explosions in the BGS Seismic Database in the Area of Beaufort’s Dyke], 1992-2004' (2005) (referenced in British Geological Survey Commissioned Report, CR/05/064)