The Merchantman was an independent freighter operating in the late 23rd century.
In 2285 the Klingon operative Valkris managed to obtain a copy of Admiral James T. Kirk's report on his most recent voyage, which included a summary of the Genesis Project. She traveled on board the Merchantman to rendezvous with Commander Kruge's Bird-of-Prey. Valkris transmitted Kirk's report to Kruge, and stated that he would find the report useful. Upon realizing that she had seen the data Kruge had his ship to attack and destroy the Merchantman.
Although Kruge and his crew believed that the crew was killed in the attack, some of the crew managed to make it to escape pods before the ship was destroyed. They were later rescued by Starfleet, and reported that they had been attacked by a Klingon vessel. (Novelization of Star Trek III: The Search for Spock)