A Royal Marines helicopter hovers over the River Thames during an exercise in preparation for providing security during the London 2012 Olympic Games. (Finbarr O’Reilly/Reuters)

To spread around the surveillance, police are offering free counter-terrorism training to mobile food vendors to help spot suspects during the Olympics.

Along with the vendors, London will have 12,000 police officers on duty, plus 13,500 troops deployed on land, at sea and in the skies, the Associated Press reports.

Terrorists have struck at the Olympics in the past, including the 1972 Munich Olympics when 11 Israeli athletes and coaches were killed and the 1996 Atlanta Olympics when a bomb killed two people and injured more than 100.