|This article, Thermopylae-Class Troop Transport, is currently under active construction.|
Commissioned in 2483, the Thermopylae-class were intended as a cheap transport for UNSC Marine Corps personnel, capable of ferrying up to a regiment at a time, deploying them in combat and supporting them to a limited extent. Though relatively poorly armed, it was able to ferry supplies and personnel to planetary theatres of combat via Albatross or Pelican dropship or, in rare instances, de-orbit itself to deploy itself onto the battlefield permanently as a command centre. They served effectively throughout Operation TREBUCHET, ferrying Marine Corps and Army personnel from Reach to the other troublespots throughout the Epsilon Eridani System, and would also serve in the other conflicts that would erupt afterward - 111 Tauri, Delta Pavonis, and Alpha Centauri. Given the nature of space warfare at the time, the Thermopylae's proved at the least adequate - the Insurrectionists rarely fielded warships or fighters of their own, and when they did they were often hastily retrofitted civilian ships with bolted-on weapons, little match for the sleek warship escorts that protected the Thermopylae's.
When the Covenant attacked Harvest, and began their campaign against the Outer Colonies, FLEETCOM was forced to re-evaluate the capabilities of the Thermopylae-class. Compared to other troop ships used by the Navy, such as the Phoenix- or Herald-class, the Thermopylaes were larger and able to carry more personnel, but were also larger targets. They were also poorly armed and possessed thin armour, relying on escort ships for protection - the armour was augmented, and additional CIWS turrets were added for point defence, but the Thermopylae would continue to be combat ineffective for the rest of its service life. Specialist variants were fitted with SOEIV Launch Tubes for deploying Orbital Drop Shock Troopers, perhaps the only dedicated ship class the Helljumpers warranted, but ultimately the Thermopylaes were withdrawn from frontline service in favour of better armed transports, most converted into military freighters. As the last Outer Colony fell, and the Inner Colonies came under attack, the Thermopylae's were again returned to active duty, and were organised into small groups for improved protection and the deployment of entire Divisions at a time - at Megiddo and Lefanyal, four of the Thermopylae's deployed themselves on the battlefield, not only deploying their passengers, but effectively forming the core of the UNSC main headquarters until the fall of those colonies. The last of the Thermopylae's were present at Reach and Earth when the Covenant attacked, and by the end of 2552 none were left intact.