A defense armature was an automated component, a defense mechanism, that was inside a Delphic Expanse sphere.
In 2154, a particular defense armature attacked and killed MACO soldier F. Hawkins while he and an away team with him were attempting to steal the sphere's memory core. (ENT: "The Council")
The term "defense armature" comes from the final draft script of "The Council", where it was used consistently to refer to the mechanism which kills Hawkins.