The firing of Depleted Uranium (DU) shells into the Solway Estuary began at the Kirkcudbright Training Area (KTA) near Dundrennan in 1982. Leaked government ministry documents from the 1970’s set out the early, internal government controversies over the testing of DU weapons: the scope of the radiological and chemical hazards involved, the requirements for environmental monitoring, the difficulties presented by the differences between England and Scotland and the need for secrecy given a public that ‘cannot understand’ and that opposes nuclear arms. 
Those factors play out, with variations, over the next 40 years, at least as far as can be ascertained from information in the public domain. Added to them are the mangles of government bureaucracies, the privatisation of sectors of the MOD, confusion over which department has responsibility for which activity, funding shortfalls, the misleading of Parliament and the public and changes within the civil-military nuclear industries.
The more recent tests are of the DU ‘penetrators’ at the core of CHARM3 armour piercing shells. DU is used because of its density and its pyrophoric properties. The shells are fired from British Challenger II tanks.
The shells are fired towards large target screens of canvas-like material hung on frames erected on the cliffs over the Solway Firth. Most firings pass through the targets and continue their trajectory out to sea, one estimate being 3 kilometres out, other estimates allowing for a considerably longer arc before touching the surface of the sea. The trajectory below the surface is unknown. There have been misfires and accidents, resulting in DU contamination of the land.
The places from which the firings were made or were storage areas for DU that can be found on an Ordnance Survey map include Gypsy Point, Little Raeberry, Little India, Doon Hill. The target gantries include Ballig, Chapmans, Echo and Big India.
As of 2011, it is estimated that 6,000 shells have been fired containing 30 tonnes of DU.
The circumvention by the MOD of the legally binding international laws against dumping nuclear waste into the sea under international agreements came to light in the 17 June 2004 minutes of the 36th meeting of the Depleted Uranium Firing Environmental Review Committee (DUFERC) in the following item:
‘5.6 [redacted name] stated that there could be a future problem with regard to firing into the sea as the OSPAR Agreement stated now that it was illegal to dump waste into the sea. There was some discussion surrounding the wording and [redacted name] stated that currently we worked to the D SEF Pol interpretation that the projectiles were placements not dumpings.’ 
All government reports to date have found that there are no significant consequences, no hazards presented by these firings to military personnel or members of the public, nor is there significant contamination to the marine or terrestrial environments. Reports by the World Health Organisation, the Royal Society, British Geological Survey and other government bodies find no significant contamination.
Critics of those reports find that the terms of reference for the testing and evaluation are incomplete or inaccurate, the methodologies inadequate, the timescales faulty and the research premises not fully disclosed. Reports by independent academic scientists find that the uncertainties and turbulence of the marine environment precludes definitive assessments of the hazards for marine populations or for the safety for human populations as the projectile shells corrode in the sea. 
The most recent available report on government policy (8 July 2015) states that:
‘UK policy is that depleted uranium (DU) munitions can be used in weapons because it would be wrong to deny our armed forces a legitimate and effective capability that can help them achieve their objectives as quickly and safely as possible. Claims of serious health and environmental effects by a very small number of people attract media attention but are disputed by most scientists and international agencies. Whether other countries use DU munitions or not is a matter for them.’ 
The chronology here lists events, disclosures and shifts in the monitoring and legislation of these firings. Given the secrecy which surrounds Ministry of Defence (MOD) activity, this is not complete, but each entry derives from sources which can be verified. See also references for other sources and a list of government reports available online.
This also is not the whole story. I do not know from which countries the Uranium was mined nor which countries manufactured the weapons grade Uranium from which the Depleted Uranium is a waste product. I do not know where the arms were constructed; or who the ‘Customer’ is, the agency that required these tests, whether it is the British MOD, the American military or a commercial arms manufacturer. I do not know how the MOD calibrated the results of these tests according to their military, weapons efficacy, criteria.
Too, the chronology does not include details of public responses. Nor the wider military, political and nuclear contexts and the ethical contexts in which these firings were sanctioned. These are issues dealt with in the journal section.
The information below derives primarily from the work of campaign organisations and investigative journalists interrogating the Ministry of Defence (MOD) from the 1990’s through 2014/15 and the MOD’s release of documents following Freedom of Information requests including the minutes of the Depleted Uranium Firing Environmental Review Committee (DUFERC) set up to have oversight of the firing programmes. Other sources are declassified MOD documents and reports from other statutory bodies, such as the Scottish Environment Protection Agency, and the occasional whistleblowing leak.
Land-based firings as Eskmeals, Cumbria, on land, were part of this test plan, but are not part of ‘the sea cannot be depleted’ project.
 See the journal section for the Minutes of the DUFERC meetings.
D SEF Pol is the Directorate of Safety Environment and Fire Policy (MOD).
OSPAR is the mechanism by which 15 governments, including the UK, and the EU cooperate to protect the marine environment of the North-East Atlantic. Its decisions are legally binding. OSPAR started in 1972 with the Oslo Convention against dumping and was broadened to cover land-based sources and offshore industries by the Paris Convention of 1974. These two conventions were unified, up-dated and extended by the 1992 OSPAR Convention.
 The Campaign Against Depleted Uranium (CADU), now part of the International Coalition for the Banning of Uranium Weapons (ICBUW), have pursued government transparency and accountability, as has Rob Edwards’ investigative journalism.
See references for government and academic reports.