Osler occupies perhaps one of the most unique spaces of all Federation starships. Built for a war she ultimately never took part in, her career is dotted with various problems that were ultimately never actually the fault of the ship's design, at least not for her design purpose. Consequently, though it's hard to call her a poor vessel, she is one of the most concerning ones.
The Osler's basic design owes itself to the limits of the Treaty Of Algeron, finalised in 2313 between the Federation and the Romulan Star Empire. These limits, due to concerns related to the Genesis device, outright banned cloaking devices, which were stipulated as any device which attempted to conceal the ship through the complete EM spectrum, which banned all systems in use by the Federation at the time and would go on to include phase cloaking devices. This limit was considered acceptable, as the Federation ultimately had little need nor desire for cloaking devices at the time, though most larger ships carried them as a relic of the Klingon Cold War. It was believed that this would be perfectly acceptable under all circumstances, which was great until it wasn't.
The Dominion had very much responded to the Federation's grand, luxurious flying hotels, namely the Galaxy Class, by showing absolutely no reserve in destroying them. Whilst the newer anti-Borg ships were already entering service at this point, the thought came to a ship meant to fight the Dominion, primarily by sneakily inserting the ships into Dominion forward bases and attacking them in dock. This move, considered by them to be a remarkably Romulan idea, was actually brought up by the head of San Francisco Yards, who was a noted enthusiast of old Earth submarine combat. And so, the project for the Osler was born.
Progress on the Osler was defined by a need to render the ship effectively completely invisible to Federation sensors, considered some of the best in the entire Galaxy, without actually rendering the ship invisible to the naked eye. This proved extremely difficult, with numerous materials tested on an iron frame, launched into space and tested against the sensors of the USS Nova. Eventually a classified composite material did pass the test, which can be said to have been a deep shade of black.
This material was glued to a space frame approximately 105 metres long. Sporting a line of red lights to ensure the ship was visible and thus Algeron-compliant the ship, despite its tactical orientation, only had a dual torpedo launcher and singly Type X phaser. This armament was extremely light but done in the context of the ship's requirements. Notably the ship was only intended to fire tricobalt devices, with the intent to quietly fire a tricobalt device at the target whilst its shields are down and warp away quickly. Her torpedoes were specially designed to appear as specs of dust, making it appear the enemy ship wasn't under attack until it exploded, by which point the Osler would have already left. Internally the ship was powered by an SSWR-XL-D warp core, modified to minimise radiation and heat output. The ship's warp drive was rated to cruise at Warp 7 and hit a peak of Warp 9.1, with the ability to alter its warp field to appear as anything from a shuttle to a Klingon Bird Of Prey. Due to the stealth requirements however, the ship only had navigational shields and lacked defensive shielding, something thought to not be an issue as she was never intended to fight. All in all the ship had the makings of an excellent stealth vessel, and yet remained totally compliant with the treaty of Algeron.
The ship was ready for trials by March 2375, and performed excellently in her trials. Unfortunately the war came to an end only 3 months later, before the ship could rotate out to Deep Space 9. Consequently Starfleet was left with a ship they ultimately had no use for, and so Osler remained in dock until Starfleet Medical Division 14 petitioned for a dedicated transport vessel to The Farm, a medical facility on Endicronimas V. As Osler was available and lacking in a role, she was given to Division 14, and put under the command of Elat K'ven, an Edosian medical specialist. The ship would remain in Division 14's hands until 2380, when the ship's passengers mutinied citing the poor conditions on board. The mutiny ended when the ship arrived at The Farm, before the mutineers could kill an ensign from the USS Cerritos who'd been involved in a transporter accident, but the mutiny had put Division 14 on extreme edge as a result. Osler would consequently be retired after just 3 years of service, and replaced with a modified Olympic class transport.
Osler remained in this state of retirement until 2385, when the ship was requisitioned by admiral Picard for the boldest attempt at an evacuation of Romulus, being readied at Utopia Planetia shipyards alongside a large fleet of Wallenberg class tugs and a small number of older vessels, including the USS Helios. Having been landed on the surface of Mars when the Synthetic Androids went rogue, she loaded up with Martian Civilians and Starfleet Personnel and fled, relying on her stealth to avoid detection. Among the survivors were notably Commodore La Forge and Admiral Jellicoe, who'd been curious about the vessel at the time. The ship successfully made it to the Admiralty Emergency Site, formerly Deep Space K-7, and reported news of the massacre to the Fleet when she arrived, as well as that La Forge and Jellicoe were alive. Consequently the ship was kept on standby at K-7 and remains in this largely symbolic position, having finally done something remarkable. Despite the lack of need for her, she remains a valued ship in the fleet if only for that.