WASHINGTON (CNN) -- Three Air Force officers fell asleep while in control of an electronic component that contained old launch codes for nuclear intercontinental ballistic missiles, a violation of procedure, Air Force officials said Thursday.
The Air Force said the launch codes had been deactivated before the incident, but it was still a violation of protocol, prompting an investigation.
It is the fourth incident in the past year involving problems with secure handling of components of America's nuclear weapons.
The incident occurred July 12, during the changing out of components used to facilitate secure communications between an underground missile-control facility and missile silos near Minot Air Force Base in North Dakota, according to Col. Dewey Ford, a spokesman for the Air Force Space Command in Colorado.
One of the parts, a code component, is for storage and processing. It is considered classified by the Air Force.
A code component was removed from the equipment at the remote missile-control facility and replaced with a new code component. That made the old component inoperable, but an Air Force source said old launch codes were still contained in the part.
Under standard procedure, the four-officer crew of the facility is supposed to keep the component secure until it is returned to the base. Ford said the crew took the component to a building above the facility and locked the component in a lockbox.
Then, three of the four crew members fell asleep.
This violated Air Force procedure, which calls for at least two of the crew members to remain awake while in control of the component. At the time they were asleep, the crew and the component were in a locked building that is guarded by at least one armed airman at all times. (Continued)