The UNSC Themistocles was an Orion-class assault carrier in service to the UNSC Navy with an operational history stretching as far back as the 2510s up until the Guardian Crisis. One of the first in a new line of vessels designed in response to the rising Insurrection, the Themistocles and its sister ships boasted their own production facilities which enabled them to support prolonged mass military operations on distant Outer Colonies, making them a key part of the UNSC's strategy to counter planet-wide rebellions. After 2525, these capabilities also made them critical to the Navy's efforts against Covenant, supporting entire battle groups as fleet carriers, though this role brought many into direct contact with superior Covenant forces and resulted in the destruction of most of the class.