The Arc Hammer is a long, dagger-shaped Imperial warship that was built by Kuat Drive Yards at the height of the Empire's power. It was essentially a huge, floating manufacturing facility that produced and launched Dark Troopers.
The vessel itself is nearly the equal of a Super Star Destroyer, with more weapons but weaker shields and hull, and is a powerful combat vessel in its own right, or at least it was until it was destroyed.
Being a secret facility, the factory frequently made jumps to hyperspace, and only one ship—Executor—knew its exact position at any given time. It was commanded by General Rom Mohc, who headed the Dark Trooper Project. Dark Troopers were deployed directly from the ship in their debut during the Battle of Talay.
Following the successful theft of the Death Star I plans, Rebel-allied mercenary Kyle Katarn was assigned to investigate the loss of Tak Base on Talay. While there, Kyle discovered a large gun, too cumbersome to be efficiently wielded by a regular stormtrooper.
Eventually, after investigating various secret Imperial factories and weapons scientists, he learned of the Dark Trooper Project, and snuck aboard Arc Hammer via a cargo transfer. Kyle Katarn defeat General Mohc in combat, despite the fact that Mohc had donned a Phase Three Dark Trooper unit as an exosuit. He later destroyed the ship by placing sequencer charges throughout certain exhaust ports within the ship and the Dark Trooper project was smashed.