Operation Temperer

Operation Temperer is a British government plan to deploy troops to support police officers in key locations following a major terrorist attack. It was put into effect for the first time on 23 May 2017 following the bombing of an Ariana Grande concert at Manchester Arena, and for a second time following the 2017 Parsons Green bombing.

Background
The plan provides for up to 5,100 service personnel from all 3 services to be deployed to "augment armed police officers engaged in protective security duties" at key sites in the United Kingdom. According to government sources cited by the Daily Telegraph, it would only be triggered following a COBRA meeting. The plan was put in place following the January 2015 Île-de-France attacks in France. It was intended to be kept secret, but was accidentally disclosed in July 2015 after being inadvertently uploaded to the website of the National Police Chiefs' Council. It was said to have been contentious with the Army leadership, due to concerns about it causing overstretch, morale problems and difficulties with deciding when to end the operation.

The British armed forces have previously deployed to support the police, most notably during the Troubles in Northern Ireland when 21,000 troops were deployed to assist the Royal Ulster Constabulary in Operation Banner. In 2003, Tony Blair's government temporarily deployed 450 troops to Heathrow Airport and other London locations during a period of heightened terrorist threat.

Other European countries have also deployed troops to guard against terrorist threats in cities; France has deployed over 10,000 troops under Operation Sentinelle since the January 2015 attacks in the Paris region, and Italy also deployed 4,800 troops in Rome and other cities in February 2015.

2017 Manchester Arena bombing
The plan was activated for the first time on 23 May 2017 following the Manchester Arena bombing. Prime Minister Theresa May announced that the police had asked for military support and the request had been approved by Sir Michael Fallon, the Secretary of State for Defence. The operation remained in force until the end of the bank holiday weekend, despite the threat level being reduced from critical to severe on the 27th of May.

The website Warfare.Today identified the military deployment as involving units from the Foot Guards, the 2nd Battalion, The Parachute Regiment (2 PARA) and the Royal Artillery, with additional assistance expected from the Royal Marines the RAF Regiment and the RAF Police.

2017 Parsons Green bombing
The operation was activated again on 15 September 2017 when the threat level was raised to critical in the aftermath of the 2017 Parsons Green bombing, with military personnel replacing police officers on armed guarding duties.

Foreign Equivalents
Operation Vigilant Guardian is a similar operation by the Belgian army.

Operation Sentinel is the French Army equivalent.