The Action VI transport, sometimes referred to as the bulk transport, was a popular freighter built by Corellian Engineering Corporation.
Action VI transports typically operated in convoys or in well patrolled areas of space, since they lacked even the most basic forms of self-defensive measures, and had to rely on protection from other capital ships. The only reason they were used by the Galactic Empire, was because they were quite inexpensive (relative to Imperial wealth).
The Rebel Alliance also employed these cargo vessels, often as personnel carriers, but in much smaller quantities since they were far more expensive than GR-75 medium transports. Most Action VIs were stolen from the Empire.
Pirates often modified Action VI ships into "interceptor frigates" capable of combatting starfighters and corvettes.