The Thermopylae appears in the water to the east of Port Pryor after the mission Gang Bang. While it is shown during a cutscene during that mission, the view shown during the cutscene is impossible and the carrier itself is not present until the mission has been completed.
Her appearance signals the first deployment of STAG troops into the city.
About two-thirds into Saints Row: The Third, Shaundi is kidnapped by Kia and taken prisoner aboard the Thermopylae.
The Protagonist infiltrates the ship while disguised as Cyrus Temple and using Pierce and Viola as prisoners. The mission takes place in a normally inaccessible interior, which includes the bridge, a brig and a hangar bay. After his cover is blown, The Protagonist sabotages the Thermopylae's reactor and escapes via a VTOL transport. The massive warship explodes, splitting in half and partially sinking in the waters of Steelport.
The Thermopylae is a massive aircraft carrier loaded with advanced military hardware, primarily shown carrying F-69 VTOLs and Condor transports, along with a substantial complement of STAG troops; she also carries the STAG prefabricated bases, tanks and light vehicles seen being deployed around Steelport, though it is not clear how these are transported or what by. The vessel is Cyrus Temple's mobile command centre, and it is implied the entire STAG force in Steelport was deployed from the Thermopylae.
While they have no impact on gameplay, the Thermopylae also has a substantial number of missile batteries located along her flanks and two large triple launchers on the bow.
The carrier is an unusual design with a forward-facing, partly covered launch deck and covered hangars under a pair of short-take-off strips; behind these is a small secondary island or forward control tower. Behind this is a slanted recovery deck with two helipads on one side and a massive elevator on the other. The carrier's main island and radar tower are located astern. The long strips at the bow and recovery deck imply the Thermopylae is designed to launch CATOBAR aircraft. However, throughout the game, the Thermopylae was only seen carrying F-69's. It also lack the catapult and arresting equipment seen in a CATOBAR carrier which means it's most likely can only operate V/STOL aircrafts like the Condor or F-69.
- The Thermopylae is always empty outside missions, with no personnel or aircraft visible on the deck. Some STAG troops will spawn due to Notoriety.
- Approaching the Thermopylae outside the mission "My Name is Cyrus Temple" triggers an instant level 5 police Notoriety. Approaching the wreck after the mission incurs no Notoriety.
- At any point after the mission "My Name is Cyrus Temple", it can be seen half sunken in the same location.
- Falling through the map shows the sunken Thermopylae is actually two complete Thermopylae models, one for each half.
- The Battle of Thermopylae was a battle between allied Greece city-states against the invading army of Persia.
- The Thermopylae has a big ID number on the top of her island - "01" and the Daedalus has a similar large "02". This may indicate that these are the first two ships in the STAG fleet; the alternative would be that there are two Daedalus carriers. Confusingly, the number on Thermopylae's main runway is "00".
- There is a Builder's Plaque at the end of the runway, which reads "STAG carrier 001", "Surrender not unto thine enemy", "SJRT 150307", "HJF 210910", "Constructed under Volition, Champaign Shipyards, IL".
- It is possible to mod the PC version to replace the sunken Thermopylae with the original version.
- Following the sinking of the Thermopylae, Jane Valderama states in a breaking newscast that casualties were surprisingly light. This could be due to the fact that the halves of the ship remained largely intact and only partially submerged. However, Valderama also called her newscast as "military approved news", possibly indicating STAG manipulated the news for moral/propaganda reasons.
- The newscast also reveals that the carrier is nuclear powered like all modern US carriers