From FreeSpace Wiki
FS1 Tech Room Description
The TAC 1 (Called the TacOne by most pilots) is a heavily armored container, usually for carrying volatile or dangerous substances. It is also the preferred supply container for use in front line operations.
FS2 Tech Room Description
The TAC 1 is a very heavily armored type of Terran cargo container. It is most often used to hold delicate or valuable cargoes. TAC 1s are generally found in front-line operations in which protection from enemy attacks is a primary consideration.