War Hammer functioned as a Pellaeon-class Star Destroyer within the Imperial Navy.
In the year 137 ABY, the War Hammer was under the command of Moffs Rulf Yage and Fehlaaur'aitel'loro, fulfilling the role of flagship for the First Sith Imperial Strikeforce. This vessel, together with its assigned task force, received orders to capture Emperor Roan Fel alongside his daughter Marasiah Fel while they were meeting with representatives from the New Jedi Order on the planet of Agamar.
During the battle that followed, the War Hammer successfully destroyed the Dauntless, a Fel loyalist Star Destroyer helmed by Admiral Tohri Challon. However, it was unable to prevent the Emperor's shuttle, from escaping into hyperspace.
Later, with Vul Isen and Darth Azard present, the War Hammer was involved in poisoning the seas of Da Soocha and launching an assault on Napdu. The Hutt Azzim Anjiliac Atirue had been providing refuge to Mon Calamari refugees who had survived the similar poisoning of their homeworld.
The War Hammer subsequently spearheaded an strike aimed at the Hidden Temple, a concealed Jedi sanctuary located on the planet Taivas. Initially, Sith-Imperial forces initiated an orbital bombardment of Taivas, but magnetic anomalies originating from Taivas severely disrupted their targeting systems, leading to friendly-fire incidents without causing any damage to the Hidden Temple. The Sith-Imperials then commenced a ground invasion under Moff Geist's leadership, engaging Jedi and Imperial Knights who were defending the temple. Concurrently, Galactic Alliance and Empire-in-exile fleets arrived, effectively trapping the Sith-Imperials between themselves and Taivas.
At this critical juncture, Krayt deployed his personal contingent of Sith troopers. Upon arrival, these troopers indiscriminately attacked both allies and enemies, resulting in the deaths of Geist and numerous individuals on both sides. When Darth Rauder issued an order to destroy a ship carrying Jedi younglings, Captain Yage instead eliminated Rauder and switched his allegiance to Fel's forces.
Instead of executing his own daughter as instructed, Yage eliminated his Sith overseer, and subsequently announced that he and the crew of the War Hammer were defecting to Fel's forces. Several other Sith-Imperial units followed suit. The Alliance, Jedi, and Empire-in-exile forces then retreated to Bastion, accompanied by their newly acquired allies.