James Tait Praefke, 37, was helping a guard retrieve lunches for other brig inmates on Sunday afternoon when the guard somehow lost track of him, said Lt. Cmdr. John Daniels, spokesman for Navy Region Northwest.

Praefke was arrested in February as he tried to clear Customs upon returning from deployment in support of military actions in Afghanistan, Daniels said. A bomb-sniffing dog detected a grenade and other explosives in one of his bags; he was court-martialed, convicted and sentenced to three years last month.

"He had no legitimate reason to have that," Daniels said.

A wanted poster released by the Naval Criminal Investigative Service warned that Praefke should be considered armed, dangerous and likely to resist arrest - though Daniels said officials have no evidence he is in fact armed.

The poster said he has a history of weapons use, domestic violence and driving under the influence; that he espouses pro-militia, anti-government views; and that he has experience making bombs. The latter information came from interviews with those who know him, Daniels said.

Praefke was described as 6-foot-3 and 220 pounds, with green eyes and red hair. He was last seen wearing desert camouflage.

He is an aviation electrician based at Naval Air Station Whidbey Island.