UNSC Southern Cross

"If there's one thing I know, it is that the Endo is a survivor. She has endured the worst the Covenant can throw at her, and while it may have taken some time, she eventually came back asking for more. And now that she has been rebuilt from bow to stern, I expect that spirit to live on for decades more; and when she finally meets the end, she, nor her crew, will not go quietly."

- Commander Tom Žagar, at the Endeavour 's second recommissioning ceremony.

The UNSC Endeavour, nicknamed the Heat Wave, is a venerable Beagle-class assault destroyer, and one of two ships to have participated in the Harvest Campaign and the Siege of Sol. The latest in a lineage that hailed back to the seventeenth century, the Endeavour is one of thirty-five destroyers built to trial the installation of state-of-the-art hangar facilities on light-tonnage warships. While still possessing two full-sized fusion reactors, a relatively-high acceleration and as thick a hull as the baseline class, its armaments were lacking thanks to the removal of several Archer missile pods and the down-scaling of its Magnetic Accelerator Cannons. Despite these significant drawbacks, it remained a solid vessel which outlived the sisters it was built alongside.

Specifications
Like all Beagle-class destroyers, the UNSC Endeavour shares most of its hull and superstructure design with the Halberd-class destroyer. At 480 meters in length, it was only five meters shorter than the design it was based on. Past its arrowhead bow, the differences are minimal. This mainly involved replacing certain areas of the hull with 400 millimeters of grapheel armor, which while cheaper, was not as strong nor as light as titanium-A1. The bow is slightly different, with a larger hangar bay that is half-again as large as on its more common counterparts, and a smaller upper hull. The hangar is divided into two sections; a long flight deck that is located on the upper floor, and a general-purpose bay that accommodated both dropships and ground vehicles on the lower one. Both decks use different airlocks, so they can launch and receive different squadrons at the same time. However, only aircraft entering the front hangar door can benefit from the advanced gravitic breaking system. The upper plate on the bow that ran between the raised plates of titanium-A battleplate is unusual in that had a series of automated elevators and armatures that could rearm and refuel up to three space fighters in the middle of battle. Intended as a forward-thinking feature, it was hoped that the UNSC would introduce a smaller interceptor model to take advantage of it. No such aircraft would ever reach the light of day, so the system lies unused. In homage to its maritime namesakes, the Endeavour is often seen sporting red-or-blue war paint resembling waves on its bow and wings.

Armament
The UNSC Endeavour 's primary ship-to-ship armament consisted of a fixed 27F11B6 MAC battery, which was selected over heavier gun systems because of its smaller, lighter construction. Rather than focusing on raw firepower, this battery relied on smaller shells which did not require as much electricity to accelerate to high speeds. This meant it was quick to charge and fire, and also gave the Endeavour a further reach to hit opponents; this emphasis was felt to be more suitable against the small, nimble opponents that it was likely to face. It was made up of two coilguns of different calibers; a 647mm barrel and a smaller 400mm model. The larger barrel is only used for short-ranged skirmishes, as it could only fire unguided kinetic kill vehicles at slower velocities - issues which did not apply to its smaller partner.

Backing this up was a formidable network of secondary weapons, mixed between missiles and naval autocannons. This tier not only acted as the destroyer's lighter anti-ship component, but it also fulfilled its need for a heavy air defense suite as well. The most numerous of these was its 18 pods of M58 Archer missile pods, although the exact number would gradually increase over its lifespan. These were general-purpose missiles that could be fitted with a wide variety of warheads to drastically change their purpose. For example, those fitted with M58E decoy warheads were used to draw fire away from enemy point defenses. Each pod had five silos, allowing the Endeavour to fire off a salvo of 90 missiles at once. However, despite their numbers, these were easily defeated by Covenant pulse lasers. Eight turrets of twin M66 Sentry 279mm/36 cal naval autocannons were also installed, each installed on high-elevation Mark XIV mounts. These were fairly adaptable weapons on a warship, able to dynamically switch targets between enemy warships, incoming space fighters, and engage in planetary bombardment. They were particularly effective at overwhelming energy shields, especially when they concentrate their fire in a small region.

To protect itself from missiles and enemy fighters, the UNSC Endeavour boasted a mixed armament of point defense guns. These were the last line of defense, when enemy fighters had penetrated its countermeasures and anticraft missiles and impact was now assured; as such, they were all very fast to fire and automated to ensure accuracy. Originally, this complement was quite modest, with three quad M870 Rampart 50mm/50 cal cannons and 19 M710 Bulwark 25mm/60 cal guns there to answer its needs. The Ramparts were positioned in key positions to provide an all-encompassing screen against fighters, while the Bulwarks were concentrated around critical areas to defeat missiles. In time, however, its numbers would increase to combat the effectiveness of Covenant plasma missiles and strikecraft.

There were also two large launchers that were used to carry the heavy M81273 Stormbreaker fusion rockets. Little more than a high-performance fusion drive and its fuel cell, this was by far the longest-ranged and heaviest-hitting weapon that the Endeavour boasted. Within a short time, it could reach velocities that crossed hundreds of kilometers within a second, and their kinetic warheads inflicted mortal wounds on anything that it happened to hit. These were rarely used, however, as their unguided design meant that they could rarely hit most mobile targets except when they were carefully aimed and fired. They were also hugely ineffective against energy shields, though they were still carried to make up for the destroyer's lackluster MACs.

The 2553 refit had completely changed this. The twin MACs were now the Mark IX, light coil MACs, which were a total upgrade over the old Series-2. Most significantly, they recycled about 35% of the energy used in the firing process back into the capacitors, enough to allow it to fire an extra shot per charge. The venerable M66 Sentries were finally removed and replaced with triple-turrets equipped with the new M74 Sentry system. M58 Archer missile pods were still present, but their numbers had been increased to 24 pods. The refitted Endeavour was bristling with dedicated anti-fighter weaponry: 48 cells of M340A4 Streak missiles, 8 M910 Rampart 105mm guns, and no less than 120 M710 Bulwark 25mm guns were present to obliterate any space fighter attack. Two silos for the Ragnarok-class nuclear missiles, each with a 40-megaton nuclear fusion warhead, replaced the fusion rocket turrets that were fitted. These were considered weapons of last resort against opponents that significantly outclassed the destroyer, and their EMP qualities made them much more viable against Covenant warships. All these changes leaned the destroyer much closer to the air defense role than it ever did before.

Refits
"What you are looking at is the last original part of the ship. Every other wall, beam, and electronic has been replaced or rebuilt three-times over."

- Petty Officer, 3rd class Michael 'Stuck' Bennet

As a former CMA warship, the Endeavour was typically passed over by UNSC officials when it came to upgrades, with any improvements made coming from reclaimed parts that belonged to scrapped vessels. This was partly fueled by their disapproval in combining the roles of destroyer and transport, as it was not able to fulfill either role as well as many other vessels already in service. However, as it continued to survive engagements with the Covenant, refits were eventually authorized that steadily built upon its capabilities, with these often being implemented between large-scale repairs.

By 2532, the Endeavour had received a small suite of improvements, as five years of constant action would obviously cause severe wear on its systems. While most of its systems replacements were minor and hardly affected its performance, with its powerplant, electronics, and even its superstructure being modified to some capacity, two significant changes were made. The first was the installation of a TN-91sy/n Triad targeting suite taken from the, an older computer network that allowed for better coordination of nearby Archer missile swarms and plotted more accurate fire from its naval autocannon battery. The second was a controversial array of radiators at exposed parts of the ship, which while it enabled the Endeavour to overclock its reactor and engines well above their designed limits, left holes in its armor that was never fully addressed over its lifespan. The only other noteworthy change was the increased complement of point defense guns, in a desperate attempt to better protect it from plasma torpedoes and the unexpectedly-resilient Covenant strikecraft. Because the shipwrights had to rely on whatever weapons were available, it was not composed of one homogeneous type of turret, including others such as the M810 Helix and various models of Rampart guns. A number of other weapon systems were temporarily fitted - the Endeavour at one point boasted seven silos for M280 Ares missiles sloppily fitted onto its keel, which were so rarely rearmed that these were removed during the 2532 refit.

In 2532, after suffering extensive damage following the Battle of New Tharsis, the Endeavour limped to the regional shipyards of Passage, where it underwent its first major refit. This was an expansive affair, involving the modification of vital internal equipment, the movement or mutation of its armor and hull, and the removal of dozens of makeshift repairs made over the last seven years. Most prominently, its forward bow was angled downwards and expanded in size, originally to allow for the installation of a third MAC. However, high demand for such weapons saw the space being given over to supercapacitors, munition storage, and more accommodations for Marines and pilots. Personnel assigned here were nicknamed the 'poundees,' as the firing of the MACs would rock or pound the entire deck when they fired. The last change were the 8 quad M112 Viper 375mm/26 cal naval coilguns which were fitted beneath the primary MAC, offering a substantial increase in firepower.

No new major refits would occur between 2532 and 2552, as older material from the CMA had been quickly expended during the remaining battles in the Outer Colonies, while new material was diverted to the construction of new starships. Once again, any changes were made during repairs, which typically had been higher-quality than those that had been made before. An additional six M58 Archer missiles were added, while 48 M340A4 Streak missile silos provided enhanced counter-fighter defense. Various improvements over time strengthened the hull, and the ineffective VEIL jamming suite was finally removed and replaced with a Mark XII GREY MIST wide-spectrum jamming computer. The engines and fusion reactors had been exchanged on no less than four occasions. The newest ones, four ILT-DTF-9 fusion drives, were secondary units that were taken from a scuttled heavy cruiser, and resulted in a thrust increase of 45% over the original models fitted onto the Endeavour.

After the Human-Covenant War, the UNSC Navy authorized a series of enhancements to first fulfil its need as a test vessel for Project SPHINX, and later expanded into a full-blown rebuild in 2554. Almost every single component of the destroyer was gutted and replaced, which drastically increased its performance in all areas and made it competitive with far more modern warships. While too expansive to list each change individually, there were some highlights. Under SPHINX, the Endeavour received a Kaalt Nu-pattern borer, a small Covenant-built faster-than-light engine. This changed the destroyer's role into a rapid response and messenger ship, as it could effortlessly outpace even the newest CODEN drives that were just entering service. It was also under the program that a Rutherford DIS-3081b compound fusion reactor was installed, a completely-new powerplant that was a scaled-down version of the model fitted onto the UNSC Pillar of Autumn. This allowed the Endeavour to overclock its reactor by over 300% for short periods, as it did not have the advanced cooling system to nullify overheating.

Construction and commissioning
The destroyer that would be christened the Endeavour first began construction in orbit of Chi Rho by the local construction company Diadel Systems, who had been subcontracted by SinoViet Heavy Machinery to construct a number of modified destroyers for the Colonial Military Administration. It was first laid down on August 22, 2518 as the third of the thirteen destroyers built of its batch, which ended with the completion of the CMA Heart of Midlothian in late-2522. As its previous two sisters allowed Diadel to identify and fix many issues with manufacturing and shipping of parts, the destroyer suffered no construction delays and even finished fabrication two months ahead of schedule. It was launched on January 27, 2519 to complete the fitting-out process.

As construction came to a close, the destroyer was subjected to a rigorous set of space trials, intended to test the operation of its systems and general integrity. This consisted of a series of hard burn accelerations, sensory tests, and low orbital passes. Although these were generally quiet affairs, the third of these trials was noteworthy. The ship was caught in an intense comet bombardment that saw shards of rock impact the destroyer's hull, which forced it to conduct extreme evasive maneuvers to escape damage. One of these turns saw it unintentionally collide with the MSV Ivory Tower, a large maintenance tug that was sent to rescue it. The ordeal would delay its commissioning, but the minimal, almost superficial extent of the damage showed that the destroyer was much more ruggedly built than was first believed by its builders. It was commissioned as the CMA Endeavour on March 19, 2519, and was delivered to the CMA a mere three days later. It then departed the Ectanus 45 system, manned by a rookie crew under the command of Lieutenant Commander Asia Vespa.

Insurrection
"Kids on Fjord fight better than you."

- Chief Warrant Officer 4 Kores Van Schalkwyk, to the Endeavour 's insurgent crew.

The CMA Endeavour first served in the 173rd frigate flotilla, a light naval unit that operated in the Lurone, Rawadi, and Rowena Sectors of FLEETCOM Sector 2. In this guise, it was primarily used to conduct light troop movement through the region, where it ferried elements of the 276th Colonial Army Battalion towards unrest hotspots on Pumice and Cadence. It lent naval support where possible, but thanks to the small-scale of the fighting, its support was generally limited to logistics and coordination. Other tasks included convoy protection duties to the habitats of Campbell's Landing, in an effort to deter losses to piracy in a navigational hazard zone around it. Most of these tasks were quiet affairs, as nobody realistically wanted to pit themselves against a Colonial Navy destroyer.

In October 2521, the Endeavour was reassigned into the 114th Rapid Strike Squadron, the largest and most active CMA naval unit in the Asgard Stratum, as a replacement for the destroyer. This reassignment was also to partially cover the refit of the carrier, with the Endeavour taking over some of its servicing duties for the four months it was in dock. Within the 114th, the destroyer was supposed to assist any starships in distress, where it would quickly move to dock and embark any crew and cargo that can be saved from disabled craft and fight off any attackers. The agricultural content of these freighters meant that it was vital that shipping losses were kept to a minimum, and the Endeavour was involved with the rescue of 19 civilian freighters and four warships during 2522 alone. However, the 114th's power meant that its escorts were responsible for tracking and hunting down any significant insurgent elements in the region, as well as reinforce any CMA garrisons that were struggling to put down unrest. For this need, the destroyer participated in putting down the insurrections of Madrigal, Green Hills, and especially Redstow VI, where it supported ground incursions with orbital strikes at the cost of escalating civilian casualties. However, the sudden increase in readiness and activity, as well as the now-notoriously low standard of training given to CMA recruits, meant that the Endeavour 's largely-inexperienced crew were seen as both incompetent and lazy. This was almost dangerously so, as it almost fired upon allied vessels on several occasions; this reputation would only be erased following the start of the Human-Covenant War.

In February 2523, Vespa stepped down as the Endeavour 's commanding officer, and was replaced by Lieutenant Commander Chi Kariuki. An ambitious officer, it was under her leadership that the destroyer became host to sympathizers of the Biko Independence Army (BIA). At first, the only assistance the crew offered were leaked communiques sent through the squadron, and Kariuki's desire to impress saw these quickly shut down. It was only through negotiations and bribery of her communications officer, Lieutenant Patryk Adamczyk, that operations escalated. Throughout the rest of the year, the Endeavour actively assisted the BIA's efforts by providing dead drops of infantry equipment and firearms, starship munitions such as Archer missiles, and even entire vehicles and dropships when possible, all of which was smuggled back to Biko. This assistance was also afforded to other Insurrectionist groups, where it misdirected CMA and UNSC forces by providing false sensor reports. It even faked the deaths of Godfrey's Commandos, one of the Secessionist Union's most elite forces, during Operation: THUNDERBIRD by quietly folding them into the crew as their own department.

All of this eventually culminated in a scandal. In early 2524, the BIA used many of the weapons they received from the Endeavour in their fifth uprising, and were swiftly put down by UNSC forces. Analysts from ONI Section One were brought in to scour through the wreckage, as well as interrogate one of the captured insurrectionists for information. While they were able to determine that the equipment was stolen from the CMA, the exact origin was ultimately unknown as their prisoner did not survive. As a result, ONI covertly seeded teams of investigators among CMA garrisons to hunt it down. One of these teams, composed of Chief Warrant Officer 4 Kores Van Schalkwyk and his Navy handler Lieutenant Theodora Papadopoulos, were officially serving as trainers for the Endeavour 's when they were captured by the ship's crew. It was only when they escaped and intercepted one of the weapons drops left behind that they obtained solid proof that connected the destroyer to not only the BIA, but also exposed the rampant insurgent activities in the region. The Endeavour was immediately suspended from operations, and its entire crew were detained and interrogated by Section 1. Many would be pressured into resigning from the CMA, LCDR Kariuki and several of the senior officers were court-martialed for negligence, and the few that were released were reassigned. The ship itself was thoroughly swept of any listening devices, and its databanks were recovered for further analysis. When it finally returned to service in January 2525, it would be under an entirely-new crew.

Covenant discovery
The CMA Endeavour 's first actions in what would become known as the Human-Covenant War occurred in May 2525, when it was sent to investigate the loss of the CMA cruiser Urban Encroachment in the Upada Sector. A four-week search was extended into six when a second starship, the CMA Empyrean Jewel, disappeared in the same region. No traces of either starship were discovered, something which led to the regional command theorizing that they had been hijacked. As a result, it was ordered to rendezvous with the frigate CMA Raltstown to escort merchants through the Asgard Stratum in hopes of deterring raids.

However, when the civilian craft of the CAA Astrography Charting Mission deployed to the Aurna Sector failed to check in, the entirety of the 114th Rapid Strike Squadron was sent in to locate them on July 13. After 16 days of searching, the Endeavour recovered Item-291X - an alien fragment that appeared to be have once been part of a ship's hull. Two days later, the destroyer met up with another CMA corvette to verify the discovery of the wreckage belonging to one of the Mission's command ships, the CAA Babyloniaca. Preliminary analysis of the damage was undertaken, where it was discovered that it had been subject to an intense bombardment of high-temperature plasma, which breached all decks and fused the propulsion systems. More importantly, the Endeavour 's weapon officers and chief engineer both noted that the damage could not have been caused by any known weapons they were aware of. The wreckage was taken back to their home base at Biko so it could be analyzed further. Both Item-291X and the Babyloniaca convinced the regional CMA command to keep the 114th Squadron in the area, as well as reassign the smaller 38th Scout Flotilla to assist them.

On October 26, the Endeavour participated in the Skirmish of CRT-99-LP. It arrived into the system to exchange supplies with the corvette CMA Johnston, only to find itself suddenly attacked by what was later identified as a. In an action lasting a minute and a half, the destroyer took several blows from the much smaller alien ship, breaching D-deck on the bow and killing four people. Meanwhile, the only hits from the human side were from a salvo of one of the Endeavour 's naval autocannons, with its missiles rendered completely by its jammers. While it did force the raider to flee, no damage was registered on the enemy ship. The destroyer immediately began a rescue of the Johnston 's 13-strong crew, although only a single comatose survivor was recovered.

The Endeavour towed the Johnston back to the nearest CMA outpost at Green Hills, where they filed an urgent report to CMA Command concerning the engagement with an unidentified alien vessel. They were instead surprised to find that they received orders by the UNSC High Command, signed by the UEG Minister of Defense, to head with best possible speed to the nearest UNSC naval base at Falaknuma in the 18 Scorpii system. Upon arrival, the two ships, along with the recently-arrived CMA Hercules, were temporarily grounded as ONI Section One teams combed over them for any intelligence on their potential adversary. These included thorough interrogations of the crews, reviewing computer readings taken during the battle, and inspecting the damage incurred to discover new insights. Repairs were halted while this process was ongoing.

In light of ONI's conclusions and the discovery of what happened to Harvest, the UNSC declared a state of emergency on November 1, forcibly placing all CMA personnel and property under its direct jurisdiction. As a result, the destroyer was rechristened the UNSC Endeavour, and major software upgrades were implement to allow it to interface with the UNSC battlenet and communications systems.

Cole Campaigns
The UNSC Endeavour, along with the other few warships that had already fought against the Covenant, were reassigned into the massing. The newly-returned Vice Admiral Preston Cole specifically requested these ships in hopes that their crews could better inform his upcoming strategies. In any case, the destroyer participated in the, where Cole's fleet attempted to destroy the single that orbited the planet. It was first tasked with screening the larger cruisers from incoming plasma fire, but then moved forward when it became clear that the fleet's countermeasures were unless against the Covenant warship. It and the other destroyers tried to take advantage of the battleship's focus on X-Ray's capital ships by swarming it, but the near-misses and glancing hits kept the Endeavour away while its shields easily withstood their fire. The entire fleet was almost about to retreat when Cole ordered the entire fleet to target a specific part of their opponent's bow, and coordinated their salvoes so they would hit at roughly the same time. This overwhelmed its shields and quickly led to its destruction, giving the UNSC its first major victory in the Human-Covenant War.

The UNSC Endeavour participated in the Battles of Green Hills and Alpha Auriga with Battle Group X-Ray, but the small size of its MACs eventually saw it transferred into a support role. Instead, between October 2526 and February 2527, it served in a wolfpack with two other Halberd-class destroyers, where they departed from Harvest to raid Covenant logistics lines. They claimed to destroy thirteen ships over that four-month period, but further success was halted when the flotilla was lured into a trap. The Endeavour was the only survivor of the bloodbath, as it was holding back from the main force when the attack occurred.

The Harvest Campaign
Once it finished repairs in June 2527, the destroyer was assigned to, who were charged supporting the invasion of Harvest. Although the system was not hotly contested by the Covenant, there were still a few holdouts that were stubbornly entrenched on its surface. Before it even arrived, the UNSC Endeavour had already saw action when it intercepted a small, lightly escorted supply ship, though after an extended chase the vessel ultimately escaped.

Once it established orbit, the destroyer supported ground offensives in the Western Edda region by providing a mixture of fire support, imaging for reconnaissance and navigation, and acting as a forward operating base away from the theatre's assault ship, the. It directly participated in Operation: RIVER DANCE, where it deployed teams of ODSTs to find and destroy known Covenant communications and sensor stations, allowing the troops below to make a surprise march on the city of Thrudheim. It directly attacked a number of smaller regions, particularly those that were protected with anti-air defenses that could keep away other frigates. The few Covenant excavations sites that were captured intact were carefully examined by ONI officers on the destroyer, although they were unable to find out what they were looking for.

In November 2527, a massive Covenant counter-attack of Harvest changed the campaign for the worst. The Covenant's Fleet of Virtuous Involution appeared in force and clashed with the UNSC's fleet for control of the system. Battle Group D began to offload as much personnel and supplies as they could before withdrawing, and the Endeavour worked with the other frigates to destroy as many of transports and fighters as they could. The Covenant retaliated in kind; a wing of 213 strikecraft attacked the destroyer and inflicted damage, but support arrived quickly enough for the Endeavour to remain operational. Large sections of Western Edda had to be abandoned as it could no longer be maintained without orbital support. Finally, on December 3, Battle Group D was forced to withdraw as three arrived to decisively remove any UNSC presence in orbit. As one of the last vessels to leave, the Endeavour was pursued by one of these destroyers, although late support from the cruiser Say My Name saved it from destruction. It was towed back to New Tharsis for repairs, unknowingly being tracked by the Covenant.

Battle of New Tharsis
The Endeavour would be reunited with the 114th Rapid Strike Squadron for the first time in three years, when the sole surviving vessel, the, limbed to New Tharsis for emergency repairs. <!--

The Years of Hell
"These are hard, trying years. We've lost so many good people, many of them close friends. It has gotten to the point where I can barely feel anything when I add their names to the casualty reports. And for what? An opportunity to retreat? Another three months of repairs? I wish we could get a good look at their backsides for once, just once."

- Excerpt from the personal log of CDR Aditya Misra, describing her brief captaincy on the Endeavour.

After emerging from repairs, the UNSC Endeavour was reunited with the 114th Rapid Strike Squadron, where it was once again placed into a combat role<!--
 * Reassigned to the 114th after leaving Cole's command.
 * Distinguished itself at Tharsis in 2531 - basically UZ's RP. It was caught at the system awaiting reinforcements, fighting against the Fleet of Harmonious Resolve. Later acted as the flagship for Commodore Admiral Ashok Raymond. Most infamously, it chased an SDV-class corvette down through the atmosphere towards their base, and directly attacked the Covenant ground base, only to be fought off. Later resisted their assault in cooperation with ground emplacements - Battle of Reglith (city), Raid on Facility Eight.
 * 2531-2535: Badly stressed during this period. Fought with the 114th at Kingston and Cadence.
 * 2535: Battle of Hollow Point occurs. The understaffed 16th Fleet, bolstered by low-strength squadrons like the 114th, were attacked by Xytan's fleet, and they were absolutely smashed. The Endeavour was one of the few ships that survived it; the sole remaining bridge officer that ordered their withdrawal, Lieutenant Govind Chaudhary, was court-marshaled for cowardice. Maybe it disappears and wages its own war on Covenant logistics lines?
 * 2537: Operation: METALLIC BLUE, an all-out assault on Covenant space by the 16th Fleet. Endeavour acts as a flotilla leader and light support ship. Operation ends horribly.
 * 2538-onwards: Endeavour is reassigned to the 14th Defense Fleet. Fought at Miridem, Heavensward, and Iota Persei.
 * 2541-2545: Shannon Hambleton takes command. Although initially inexperience, it was under her tenure that the Endeavour truly distinguished itself due to her innovative tactics using SFTEs.
 * 2548: Recalled to the core regions due to its age to protect commerce and counterinsurgency operations (basically was used as a training ship).
 * Right before the Fall of Reach, the Endeavour was undergoing an engine overhaul over Tribute when the Covenant's Combined Fleet of Righteous Immolation attacked the system. It could not launch from the drydock until the morning of August 31, as attacks on its drydock delayed efforts to ready it for combat. When it finally did launch, it supported the defense by providing Longsword support, where it protected the critical shipyards and assisted with the destruction of a CCS-class battlecruiser that assault Casbah City. Eventually, the overwhelming Covenant fleet destroyed the shipyards and forced the Endeavour and the rest of the local naval element to regroup in range of the planetary mass drivers. On September 5, while full evacuation of the colony was underway, the best five ships still intact there - the most powerful being the new heavy cruiser March on Stormwell - were secretly ordered to embark their troops and make way for Circumstance to act as a diversion for Operation: LAST STRAW. In the fourteen-hour long engagement, the battle group attempted to break through the armada that laid between them, with only the Endeavour and a single other frigate successfully reaching a position to deploy their ground forces. It was the Endeavour that ended up picking up the survivors of the failed mission, among which included the survivors of a SPARTAN-III team, and it departed the Epsilon Eridani system while under pursuit in the late hours of September 7 as it made its way for Earth.
 * Battle of Earth: Shot down during the Gulf Offensive. Later rebuilt after the war and modernized.-->

SPHINX involvement and recommissioning
In the aftermath of the Battle of Earth, UNSC engineers were sent to the Endeavour 's crash site to evaluate what components could be salvaged for new construction programs. Their analysis discovered that, aside from the keel, the overall structure of the destroyer was in surprisingly good condition, and they recommended that it be raised and brought back into service. After nearly a month of repairs, the Endeavour 's engines were fired once more and, with assistance from nearby tugs, it was led into an orbital drydock. However, work paused once it was discovered just how old many of its components were. While a carrier destroyer was considered useful, the cost of its repairs and upgrades made it unattractive to the UNSC Navy's budgetary officers, who considered selling it for scrap.

The fate of the old warship was put to rest when Project SPHINX acquired the hull. After being moved to a backup facility at Titan, the Endeavour was given patchwork repairs and converted into a technology test ship, which it would serve as for the next two years. It received Covenant antigravity plating and a small borer taken from a captured, and put through rigorous experiments that tested the borer's capabilities and reception to UNSC control systems. This included several dangerous atmosphere-to-atmosphere transitions that almost tore it apart, although improvements from SPHINX's engineers would make later trips much more comfortable and safer. It also experimented with a number of other components such as plasma torpedo silos, where it was found that the destroyer's reactor did not have the output to allow it to function. This led to them replacing it altogether with an upgraded model. The torpedo tests were a failure, as on two occasions, they failed to respond to the Endeavour 's guidance signals, while on the third the munition overcorrected and almost hit it.

With their desired experiments completed, SPHINX formally returned the Endeavour back to the Navy on September 4, 2554. Although they removed much of the equipment they installed on it, the borer was left intact in order to allow it to act as a keystone ship in UNSC fleets. The Reyes-McLees Corporation were contracted to fully modernize it at their Martian shipyards. The Endeavour was formally recommissioned and handed back to the UNSC Navy on November 18, and left the shipyard under the command of Commander Tom Žagar.

Crew
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Captains

 * CPTN Taylor Gai (January 2519 - March 2519): Commanded her during her space trials.
 * LCDR Asia Vespa (March 2519 - February 2523): Transferred to command the frigate CMA Swipe Left.
 * LCDR Chi Kariuki (February 2523 - October 2524): Court-martialed and dishonorably discharged by ONI.
 * LCDR Costică Ionescu (January 2525 - January 2526): Killed during the Second Battle of Harvest.
 * CDR Wieland Hauer (March 2526 - February 2527): Killed during the Skirmish of CP-99 system.
 * LCDR Anargul Eldar (May 2527 - 2531): Field-promoted to the rank of Commander and transferred to Naval Command of New Tharsis.
 * CDR Aditya Misra (September 2533 - July 2535): Killed during the Battle of Hollow Point.
 * CDR Shannon Hambleton (2541 - 2545): Promoted to the rank of Captain and transferred to the.
 * CDR Tom Žagar (2553 - present): Current serving CO.

Bridge officers

 * LT Patryk Adamczyk (September 2522 - October 2524): Communications officer, discharged by ONI.
 * LCDR Harry Hamilton (August 2523 - November 2529): Weapons officer, killed in action.

Miscellaneous
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 * CWO4 Kores Van Schalkwyk (March 2524 - October 2524): UNSC technical liaison and trainer, transferred following the completion of his mission.
 * LT Theodora Papadopoulos (March 2524 - October 2524): UNSC naval liason, transferred following the completion of her mission.