The UNSC Simo Häyhä is an Ares-class Battlecruiser modified with radar absorbant coating, active camouflage, and other stealth technologies attached to Battlegroup Nighthawk. The vessel is intended launch surprise attacks on enemy vessels at long ranges with its Super MAC and nuclear arsenal. The vessel also often plays the role of a heavy escort vessels for the UNSC Nighthawk. Should the stealth battlegroup be discovered, the UNSC Simo Häyhä can pick off attacking Necros vessels at long ranges, before they can get into firing range of the carrier.
The UNSC Simo Häyhä is named for Simo Häyhä, also known as the White Death, a Finnish Sniper in the 1939-40 Winter War. Simo Häyhä is the highest scoring sniper in any major war, with 505 kills. This is fitting considering the vessel's primary role as a "sniper ship", picking off heavy capital ships at a distance.