From Warhammer 40k - Lexicanum
Armed Freighters are freighters that have been outfitted with military-grade weapons batteries to help protect them while operating in dangerous areas. This extra firepower comes at a price, however, as the freighter's cargo capacity is drastically reduced in order to make room for the new equipment.
Although Armed Freighters will never be mistaken for true combat ships, they have been known to lend support to outnumbered, isolated, or otherwise desperate fleets.
- 1: Battlefleet Gothic Armada, pg. 160
- 2: Armed Freighter (Saved archive page, last accessed 30 June 2015)