Avonmouth, Bristol, 2012. The National Smelting Works produced most of the nation's mustard gas during WWI. In 2012, workers who were clearing the site for a large supermarket distribution facility reported nosebleeds and skin irritations after finding buried munitions. Post-remediation, building has recommenced. [All photos by Dara McGrath]

Worksop, Nottinghamshire, 2012. The Dukes of Newcastle took their summers here, in Robin Hood's Sherwood Forest, until 1938. Then it became a U.S. storage depot for 40,000 tons of mixed ammunition, including phosgene and mustard gas. Today it is a vast expanse of parkland, heath, and woodland under the care of The National Trust.

Whipton, Devon, 2012. This WWII-era decontamination center near Exeter was charged with aiding civilians in the event of a chemical weapons attack. The building was a printshop after the war and is now derelict.

Grangemouth, Falkirk, 2012. The airfield at Grangemouth stored bulk mustard gas and was the site of secret experiments that involved spraying the toxic agent, according to former crew. Today the site is occupied by petro-chemical giant INEOS.

Little Heath, Suffolk, 2013. Maintenance Unit 94 was a WWII Forward Filing Depot that held three 500-ton underground mustard gas storage pots. In 2009, investigators found abandoned munitions, including several large jars of mustard gas. Today the site and its buildings are used as a wood-processing facility.

Spalford Warren, Nottinghamshire, 2011. Mustard and phosphene weapons were burned here after WWII, and some areas are still fenced off today. The rest of the site is used by hikers and scientific researchers drawn to one of England's rarest habitats: a wind-blown glacial sand anomaly that supports an unusual plant community. The stumps belong to conifers transplanted by the Forest Commission in 1965 that did not take to the sandy soil.

Rhydhymwyn, Flintshire, 2015. Until 1944, this was the most secretive military installation on the British mainland — a major center for the manufacture, assembly, and storage of bulk chemical weapons. At its height, the factory employed more than 2,000 people. Mustard gas and its poorer cousin "pyro" were kept in a sprawling storage facility with units above and below ground. Atomic research and tests were conducted by British scientists whose work was later instrumental in the Manhattan Project.

Woodside, Flintshire, 2014. On a back road near the Rhydymwyn Valley Chemical Works, this was a satellite storage site for bulk chemical weapons. Today the field is used for raising grouse.

Tidworth, Wiltshire, 2014. During the Cold War, both the American and British militaries simulated biological warfare by testing dispersion patterns over large areas of their respective countries. They released compounds from aircraft, rooftops, and mobile vans, using simulants that are hazardous but supposedly non-toxic at low doses. Higher cancer rates have been observed in some areas. There were more than 750 military field trials conducted in the UK between 1946 and 1971. Zinc cadmium sulfide released at this army installation in 1960 traveled more than 100 miles downwind.

Norwich, Norfolk, 2015. In the 1963-64 Norwich Biological Trials, aircraft sprayed 120 pounds of zinc cadmium in an arc 15 miles west of town. Military scientists sampled the air throughout the region, sometimes disguised as traffic pollution monitors. The tests came to light in 2005, as Norfolk hospital officials reported esophageal cancer rates 50 percent higher than the national average.

Nidd Valley, North Yorkshire, 2014. Zinc cadmium sulphide was dispersed over this picturesque wooded valley in 1957. Today the site features 15 miles of hiking trials administered by the Woodland Trust.

RAF Yatesbury, Wiltshire, 2015. Zinc cadmium sulphide was tested at this former air force base in 1954. Redevelopment of the site into luxury apartments commenced in 2007 but collapsed the following year amidst the financial crisis.

RAF Hullvington, Wiltshire, 2015. Zinc cadmium sulphide was tested at this former air force base in 1954. Part of the site is used today for military parachute training; another part is leased as a go-kart track.

Northwich, Cheshire, 2014. The Imperial Chemical Industries plant in Northwich produced a precursor chemical for mustard gas from the 1930s to 1950s. Today the administration building houses a supermarket. Developers have submitted plans to build 300 homes on the site of the old factory.

Gruniard Island, Scotland, 2013. This island off the northwestern coast of Scotland was the site of a biological warfare test in 1942. Military scientists killed 80 sheep by detonating bombs filled with anthrax spores. The island remained closed to the public for decades. In 1981, activists affiliated with the Scottish National Liberation Army left two sealed packages of anthrax-contaminated soil outside government facilities, to protest the failure to decontaminate the site. In 1990, the island was finally opened to the public, although it remains uninhabited and locals are reluctant to visit.

Stornoway, Isle Of Lewis, Outer Hebrides, 2013. Operation Cauldron was a series of biological weapons tests that involved spraying pneumonic plague bacilli on floating pontoons a half mile offshore. Nearly 3,500 guinea pigs and 83 monkeys were subjected to this experiment in 1952. On the last day of the operation, a fishing vessel strayed into the exposure area. Two naval vessels tailed the trawler for 21 days, waiting for a distress call that could indicate a plague outbreak. No outbreak occurred, and almost all records of the incident were burnt.

Westwood, Wiltshire, 2014. Tests were conducted at this former quarry near Bath in 1950-51. The pathogen serratia marcescens was sprayed in a tunnel that had been a repository for British Museum art during WWII. Today the underground site is used for the sealed storage of documents.

Shingle Street, Suffolk, 2013. Anthrax-laden bombs were tested in 1942-43 on a pebble beach outside this small coastal hamlet, where civilians had been evacuated two years earlier. Rumors of a failed German invasion helped ward visitors away from the secret site. To this day, not all files related to the incident have been opened.

Harpur Hill, Derbyshire, 2011. In 1940, Maintenance Unit No. 28 was the biggest chemical weapons reception and storage depot in the UK. Up to 46,000 individual chemical weapons were stored on the 500-acre site and surrounding country lanes. The military facility closed in 1960, and since then the underground tunnels have been used to store cheese and alcohol and to grow mushrooms. There is also a toxic quarry lake where ordnance was tested. Known to locals as "The Blue Lagoon," it has a pH level of 11.

Porton Down, Wiltshire, 2013. Porton Down is home to the Defence Science and Technology Laboratory, one of the nation's most secretive government facilities. For nearly a century, military scientists have researched and tested new weapons here. Reportedly, they are still testing anthrax and toxic nerve agents on animals, as well as researching cannabis, Ebola, bird flu, and bubonic plague, among other activities.

Nancekuke, Cornwall, 2013. This was the main site for nerve gas production in the 1950s. Many of the contaminated buildings and equipment were dumped in quarries on the site, where they remain today. It is now a military radar station, rumored to be part of the GCHQ, the British signal intelligence agency. The Nancekuke Remediation Project is currently assessing the site to determine what is actually buried there.

Beaufort Dyke, Irish Sea, 2014. Located in a narrow sea channel between Northern Ireland and Scotland, this dyke is the world's largest marine munitions dump. An estimated 1 million tons of munitions are dumped here, including 14,500 tons of phosgene shells.

Wigg Island, Merseyside, 2013. An Imperial Chemical Industries plant at Wigg Island produced mustard gas beginning in 1938, before production was moved to Rhydymwyn. In 2002, the area was declared a nature reserve, although the highly polluted parts of the site remain off limits indefinitely, entombed in structures that resemble sarcophagi.

Lords Bridge, Cambridgeshire, 2012. Maintenance Unit No. 95 was a Forward Filing Depot with two 250-ton mustard storage pots and stocks of chemical weapons. In 1955, one of the pots exploded, vaporizing 20 tons of mustard gas; a cloud of toxic black smoke spread over the countryside. The pots were finally removed in the 1980s, and today the site houses a pumping station for the New Anglia Water Company and an astronomical observatory for the University of Cambridge.

Penclawdd, Swansea, Wales, 2012. The Ministry of Defence dropped a 30-pound anthrax bomb onto the hard beach here in 1942. It burst on contact and released a fine mist that infected test sheep, who died soon afterward. Having demonstrated the effectiveness of anthrax as a lethal agent in warfare, the military began Operation Vegetarian, producing five million units of anthrax-filled cattle cake, the nation's first biological weapon. The plan was to drop the anthrax buns into Germany's grazing pastures where cattle would eat the cakes, contract the disease, and die. However, by 1944, when the operation was ready to launch, the Allies were winning the war by conventional means. Today the ruins of the military installation lie half buried in the estuary sands.

Bowes Moor, Durham, 2013. After the Allies retreated from Dunkirk, France, in 1940, chemical weapons were brought back from the continent and stored at a remote moorland site in the north of England. In the first year, sheep were allowed to graze freely among the munitions. They quickly consumed the tarpaulins and then attempted to eat the bombs, puncturing many of the thin-cased shells. Later on, soldiers erected fences and gates to keep animals out. There are still parts of the site that are fenced off from the public and grazing sheep.

Weymouth Bay, Dorset, 2012. The Dorset Defense Trials, conducted between 1963 and 1975, involved spraying four species of live and dead bacteria from ships off the coast and from the air. When the tests were revealed, the government said it "cannot rule out conducting larger scale trials in the future to try to ensure the protection of the UK from attacks by people of states using chemical and biological weapons."

Escrick, North Yorkshire, 2012. This former mustard gas storage site is adjacent to vacation homes on the Escrick Park Estate, where the woodland is used by hikers and equestrians.

West Cottingwith, North Yorkshire, 2014. Here two large underground mustard gas pots were removed in 1991, and the WWII-era facility was leveled. Equipment used in the removal was buried in a mound at the site, where it remains today.

St. Helens, Merseyside, 2013. During WWI, the factory at Sutton Oak manufactured diphenyl chlorarsine, a precursor of mustard gas. It closed for a period but reopened some years later as a research facility. In 1932, factory employees were exposed to mustard gas to test its effect on skin. When WWII started, the nation's stockpile of mustard gas was only ten tons, and for a period of six months the entire supply came from Sutton Oak. Today the site is a vacant lot within the Abbotsfield Road Industrial Estate, halfway between Liverpool and Manchester.