The LSS Lachesis was one of the last Archigos class ships built before the project was scrapped. She was on her shakedown cruise when she was given a high-priority override on her orders and ordered a remote system deep inside Freelance space. Her orders were to form up with Task Force Daedalus and await further orders. The orders came directly from the Joint Chiefs themselves.
Upon arriving, it was clear something had gone terribly wrong. The Taskforce was already engaged with Terran ships, and both fleets were over twenty ships strong. The Lachesis immediately engaged, being ordered to help cover the lead ship's flank. She engaged as best as she could, but with an inexperienced crew and a captain unable to utilize his ship's talents, the Lachesis took multiple direct hits at point blank range, tearing through the hull and exposing the crew compartments directly to space. Most of the crew died instantly; the survivors eventually ran out of oxygen and/or heat days later. All hands onboard were lost.
The Task Force suffered near complete losses, as did the opposing force. The few survivors managed to escape in shuttles or other small craft; anyone unable to make it to a ship like that was left to die a slow, painful death.
In an agreement between both governments, this engagement was covered up an all records of the encounter were scrubbed from both sides. No attempts were made to recover ships or crews; all involved were listed as simply 'missing in action' or cover stories were created for how the ships were lost over the next few months.
Emelyn Achenson was a young woman looking to start as a privateer. She was angry and driven; she would acquire a ship and form her first crew, no matter what. She encountered rumors of this secret battle between the League and Terrans; the rumor was that if you could find where it happened, you could make enough off salvage rights to retire.
She didn't want to retire, but why settle for a retrofit civilian ship, or an abused antique warship; she could have a real military vessel. She researched Task Force Daedalus, interviewing survivors and trying to separate fiction from fact. She met two men who were also looking into finding and salvaging a ship from the Task Force. Rusty and Brown Clover were both putting the same pieces together she was, however, they had something she didn't. Rusty had once seen the wrecks of the Task Force. He'd been in a malfunctioning freighter at the time, running from a Terran patrol and his navigation system was shot. He did a blind jump and ended up on the edge of the battlefield when his subspace engine gave out. He managed to find a League LCS and scavenge some parts from it to repair his subspace engines and left; he still had a partial sensor recording, but only a rough idea of where the Task Force was.
Looking at the recording, dozens of ships could be seen. However one was front and center: the Lachesis. She still seemed to have power and from the sensor readings her engines seemed intact.
Armed with more information than she'd found in over a year, Emelyn started plotting out a search pattern to find the Lachesis. She'd seen her future ship, and she would have her. (Both Rusty and Brown Clover thought she was crazy going after a destroyer, let alone an Archigos class, but she'd made up her mind.)
After months of searching, Emelyn finally found the lost Task Force. She boarded the Lachesis, to find that even after fifteen years the ship still had auxiliary power. She was able to (with Brown Clover's help) get one of the reactors online. To her complete shock, helm control was completely functional as was her subspace engines. Emelyn piloted the ship out of the battlefield and took her to a location no one would find her.
Over the next several years, Emelyn rebuilt the Lachesis, renaming her to the Spring's Endeavour. She scavenged parts, restoring her to as close to military specification as possible. During this time she received some unexpected help. Alastair McKenzie contacted her and offered to help her both make the ship legal, and to give her a Letter of Marque, allowing her access to some military supplies in exchange for her help fighting the Terrans in Freelance space. Under the table, he would also help supply her both with missing components as well as the access codes to the computer to enable her full access to the ship.
She promptly agreed and has been using Spring's Endeavor as a privateer ship ever since.
This ship was initially created literally as a vehicle for Emelyn. It was a fun 'what-if' and a way to get my SO at the time involved; Emelyn was her character, transfered from other places. She fit well, and eventually evolved into the badass pirate she is in the story.