The basement armory is an unmarked location on the Island in 2287. It can be found beside a fuel station southeast of Radiant Crest Shrine. It has a Novice level lock.
The fuel station has a working "Open" neon sign. Feral ghouls roam the station. They are probably Aubrey Copland and his crew. Inside is a gangster's shooting gallery.
A Vim semi and trailer with a flat driver's side front tire is just south of this site. It is locked with 2 skeletons and some beverages inside. This is the hijacked Vim trailer.
A weapons workbench and a chemistry station are in the basement.
The basement armory appears only in the Fallout 4 add-on Far Harbor.