A private firm contracted to provide security at the 2012 London Olympics has apologized to Olympic officials for failing to provide all the personnel it had promised.

G4S said Saturday it is having difficulty processing applicants for the security jobs. That has prompted British government officials to order an additional 13,500 military personnel to take up security duty during the Games.

Since G4S will have to pay for the extra troops, the firm estimates it will lose between $54 million and $77 million on its Olympic security deal.

Part of the military presence at the Olympics includes the assault ship HMS Ocean, which has sailed up the River Thames to guard London. The Games begin on July 27 and will run through August 12.