Defence Review

A Defence Review is the process by which government of the United Kingdom decides upon its overall defence policy and upon the means and resources devoted to achieving its defence objectives. Such reviews can happen when political or economic factors dictate, such as upon a change of Government. The Defence Review will normally result in the publication of a policy document, styled a White Paper and released to parliament as a Command paper, setting out the broad aims, objectives, and rationale for the policy and strategy.
Post World War II Defence Reviews.
The United Kingdom governmental carries out Defence Reviews infrequently, usually upon a change of government or major political event, such as just after the Collapse of Communism. They can also be necessitated by economic crises, as in 1974 and 2010. 
British Defence Reviews since the end of World War II include:
Other Defence Policy Statements.
United Kingdom governments have also conducted policy reviews which cover specific aspects of defence but do not purport to be fundamental reappraisals of overall defence policy and strategy. Examples of these include:
Comparison with the United States.
The main difference between the United Kingdom Ministry of Defence and the United States Department of Defense as pertains to the review cycle is frequency. The U.S. DoD carries out its review, styled the Quadrennial Defense Review, on a set four-year cycle, whereas the UK MoD has no set timetable for any such review.