The UK and France have also agreed to keep at least one aircraft carrier at sea between them at any one time.

BBC: Cameron and Sarkozy hail UK-France defence treaties

The aircraft appeared to have hit at least one tree, but not any buildings directly.

CNN: 1 killed after plane crashes in Los Angeles neighborhood

The defence ministry says that to sustain a long-term operation, with a proper rotation system, it ideally likes to have at its disposal three or four ships or aircraft, and up to five army units, for every one deployed at any given time.

ECONOMIST: The army