In the Navy,small offence = the brig, big one Portsmouth.
In the Army, small offence = guardhouse, big one Leavenworth.

Dear wwh, Portsmouth Naval Prison in Kittery Maine, was closed about 30 years ago!
And yes, it's the Portsmouth Naval Shipyard and it is in Kittery, Maine. The thinking is that bases in early days of the republic were named for the nearest large city.
And as a point of interest Barracks Two for the U.S. Marine Corps is at Portsmouth N.S.
My-son-the-Major went to Command & Staff College at Fort Leavenworth which is an old post and much of it is quite beautiful. They have a Museum on post if you're in Kansas and interested militariana.