From the Hampton Roads Pilot Online article "Shipyards, military bases face security breaches":

A Mexican worker used forged documents to obtain work in Hampton Roads and was caught.

Normally, such an arrest wouldn't warrant headlines. But when the illegal immigrant is cuffed on the deck of a Navy amphibious assault ship, the story takes on a more urgent meaning.

Since the terrorist attacks on Sept. 11, 2001, at least 52 illegal workers have been arrested at Hampton Roads' ports, shipyards and military installations, according to court records and news accounts. The number could be higher, because law enforcement agencies don't keep count...

The article goes on to provide a summary of many of those cases, and it includes more information on what those who want to hire legal workers are up against.

See also "[Navy] Base security scrutinized over illegal-immigrant workers" and "Doing the high security jobs Americans won't do". In the first article, a contractor might have hired people who were not just illegal aliens, but were members of a Central American gang. The same gang featured in "Al-Qaida meets with Central American gang, lawmaker says."