- "Show them the power of the Spiridus. Ready the main cannon!"
- ― Original Spiridus commander
The Spiridus was first deployed in the Valahia's initial assault of Tokyo on November 15. The aircraft began its attack on the capital by firing its railgun Balaur, doing massive damage in Tokyo Bay. Soon thereafter, Martinez Security's Antares and Rigel Squadrons arrived to the area, and assisted by the Japan Self-Defense Forces, fought off the Valahia's attack. Thanks to a structural analysis, they were able to exploit an internal weakness in the aircraft's design; as the Balaur recharged, Antares managed to destroy the Spiridus' rear heat vent, causing the Balaur's fire control system to go offline, forcing the aircraft to flee from Tokyo, leaving the PMC aces to deal with enemy fighters.
Two months after the Tokyo incident, the Spiridus was sighted flying over the Nile River region of Egypt. Subsequent searches did not find any traces of the aircraft's presence, instead revealing a Valahia base set along the river.
The Spiridus remained out of the spotlight until March 21, where it spearheaded the Valahia's promised assault of London. Antares Squadron was dispatched to the capital to destroy the aircraft once and for all. By the time they got there, the Spiridus revealed a brand new weapon called "electrolaser cannon", an energy weapon using ionised air as a means to use concentrared high voltage discharges. Despite its power, the AG cannons was eventually overpowered by Antares. The commander, probably becoming desperate, decided to unleash its AA weapons and its ultimate AA defense: an AA electrolaser cannon.
However, its fire control units were rendered useless, leaving the AA cannon to defend the dying ship. The ship, at the moment in time, had sustained severe damage, leaving the cannon itself defenseless against external attacks. Antares destroyed the Balaur's rear heat vent while it was recharging the railgun, dealing the final blow that would doom the ship. The destruction of its AA weapons and the cannon damaged the Spiridus beyond its limits, disabled the aircraft's main engines and causing its fuel tanks to explode. Seeing that the ship was doomed, the captain ordered the crew to fire the Balaur at the capitol building (presumed to be the Westminister Palace), however the aircraft began falling towards the city, safely crashing into the River Thames.
A second Spiridus, unofficially named "Spiridus II", was built by the Golden Axe Plan Private Army in their preparations to attack San Francisco in the final stage of the Golden Axe Plan. The aircraft was hidden in Lake Tahoe, while the main force was stationed at an old airport in Sierra Nevada. Now operating outside the IUPF's jurisdiction, Antares Squadron intercepted the Spiridus II over Tahoe. This model has several design differences with the original Spiridus, such as the capability to launch Hi-TASM thermobaric missiles and a unique "READS" electromagnetic shield protecting the ship's upper hull from enemy fire. During their battle, Antares was assisted by the ground forces from Martinez Security, who launched powerful missiles on the Spiridus from Nevada, made the READS system temporarily disabled and giving the pilot a chance to destroy the Hi-TASM launch ports and saving the friendly ground forces.
The ship's READS electromagnetic shield and Hi-TASM ports were eventually destroyed, forcing the aircraft to retreat west as it deployed IRCMs and electrolaser cannon. Both IRCMs and the cannon were destroyed, and the aircraft was finally shot down with a large missile, causing it to lose control and crash into Lake Tahoe and removing the threat of the Spiridus for good.
This fortress is the main weapon of the insurgent group Valahia, and has a sister ship, the lightly-armed Orgoi. It was shot down over London, but the Golden Axe Plan Private Army rebuilt it near Lake Tahoe, Nevada. It had a minor weapons improvement, such as IRCM spheres (identical in function to the High-Powered Microwave of Skies of Deception), Hi-TASM missiles tested over the Adriatic Sea, and READS, an electromagnetic shield around the Hi-TASM launchers that effectively defended against everything except ballistic missiles. It was also shot down.
Weapons of this aerial fortress include an aerial version of the railgun Balaur, three air to ground electrolaser cannons, one anti-air electrolaser cannon, Hi-TASMs (on the Spiridus II), conventional AA weapons, AA guns, AAMs, and a unique IRCM (mounted on the Spiridus II) which blocks all missiles and can apparently do damage in the same manner as the HPM mounted on Fenrir in Ace Combat X.
The second Spiridus was also equipped with a defense system which emitted waves of electromagnetic radiation to deter missiles and bullets from the launch ports of the Hi-TASM known as READS, a large enough missile however, such as the ones launched by the ground forces in Nevada, can temporarily disable READS, giving a pilot the chance to attack the Hi-TASM launch ports.
- The player battles a total of two Spiridus in the game.
- The Spiridus bears a striking similarity to Ace Combat 3: Electrospheres X-49 Night Raven. This can be explained by the fact that the game's design director was also the one from AC3.
- The Spiridus is the airborne fortress with the highest number of weapons in the series, with a total of five. By comparison, the Gleipnir has two.
- The Spiridus I's descent into the Thames River is quite reminiscent of the Gleipnir's crashlandng in the Santa Elva river in Ace Combat X.
- The word 'Spiriduș' (read 'Spee-ree-doosh') means goblin, pixy, puck(fairy) or imp in Romanian.
- The Spiridus is only one of two airborne fortresses able to do VTOL flying.
- The Spiridus has a strange ability of flipping halfway up and its face is looking at the sky. This is seen 2 times in the mission where Antares Squadron has to destroy the Electrolaser Cannon installed on the Spiridus. There is also a glitch if you destroy all the FCUs quickly it can flip the opposite way and it is flying with its Electrolaser Cannon pointing on the ground. Unfortunately it glitches out and then reverts back to its original position.