From the Navy News website:
...In all, some 17,000 military personnel are committed to the Olympic and Paralympic events – 2,600 each from the Navy and RAF, 11,800 from the Army.
And of those 17,000 personnel, 1,600 are involved in ensuring the skies of London are safe, among them the 53 air and ground crew from 854 NAS and their Sea King Mk7 Airborne Surveillance and Control, fresh from front-line duties in Afghanistan.