From Star Trek Online Geekipedia
The Ambassador Class starships was is a federation starships designed and built in the early 24th century.
During the 2320's the Ambassador class was developed as a replacement for the ageing Excelsior Class and Constellation class as Starfleets front line Explorer type vessel. Several innovative new features were included in the new design, most notably for the diplomatic and scientific missions. The USS Ambassador included high quality guest quarters and was equipped with elaborate conference facilities. Many of these areas were capable of maintaining a wide range of environments, a vital prerequisite for a vessel which would spend a great deal of its life dealing with non standard life forms. These facilities allowed her to host a much wider range of diplomatic functions than the more cramped Excelsior class, although it did lead to the class being dubbed "space hotels" in some quarters.
The scientific facilities of the Ambassador class were equally well equipped. The ships contained the most powerful space borne sensor arrays of their time, including eighteen modular sensor pallets for mission specific equipment. Twenty eight large dedicated laboratory facilities are included in the ship, along with facilities to convert three of the cargo bays to hold extra scientific equipment if necessary. This gave the Ambassador an estimated 450% increase in research capabilities over an Excelsior class vessel.
While the primary purpose of a starship is exploratory and scientific, the Ambassador class also has teeth. The class introduced phaser arrays to Starfleet in place of the ball turret phasers carried by previous designs. This measure greatly increased the ability of the Ambassador class to fire sustained bursts, and greatly reduced the recharge and cool down times. The use of an independent power system for every group of ten emitter segments in the array triples the survivability of the array compared to a ball turret, while there are also benefits to the reaction time, greater control of thermal effects, field halos and target impact. Overall the phaser arrays of the Ambassador are over 65% more effective than ball turrets of similar power. The concept of burst firing photon torpedoes was another first; although fitted with the same number of torpedo tubes as the Excelsior class, the Ambassador's ability to fire five torpedoes at a time from each tube effectively gave her ten tubes in place of two.
After the first batch of Ambassadors was delivered, Starfleet requested a series of modifications for the second batch. The USS Yamaguchi pioneered these changes. The engineering hulls aft end was widened to allow the shuttle bay to be enlarged, and a third shuttle bay was added to the underside of the engineering hull. This allowed the Yamaguchi to handle over 30% more shuttle craft than the standard Ambassador, making the ship more effective in colony establishment and support operations or emergency evacuation scenarios.
The siting of the Ambassadors saucer forward on the neck had led to some structural problems with early members of the class. Although these had largely been fixed by modifications to the structural integrity field, the changes had led to considerable complication of the layout of the ships connecting neck structures. Starfleet took the opportunity to shift the Yamaguchis saucer section back by six metres, allowing them to eliminate return to the original SIF modification without further difficulties. The nacelles were also shifted back in order to keep them at minimum safe distance from the saucer. The bussard collectors are a different model on the Yamaguchi, with a cap on the top and bottom of the inlet system which allows a less turbulent flow into the collectors, so increasing their efficiency by 12%.
The deflector dish was modified to allow more sensor systems to be installed, and to provide additional protection at high warp speeds. Additional sensor systems were installed in the main sensor dome on the saucer section, necessitating a housing to be installed between the dome and the hull to hold the extra equipment. This allowed the sensor range and sensitivity to be increased by over 20% compared to the original Ambassador. The layout of lifeboats within the saucer section was also modified to allow increased evacuation speed in an emergency.
USS Enterprise NCC-1701-C of the Yamaguchi subtype proved highly efficient. Perhaps the most important change was the installation of a new model of impulse engine. The original Ambassadors had always been considered to have low speed and agility at impulse and the new engines provided almost 30% greater thrust, largely correcting this problem. The only exterior change caused by this alteration is that the engine exhaust is red rather than blue. The Ambassador class would prove to be highly successful in service, and all existing vessels began to upgrade to this standard from 2350. The only ship which was not so refitted was the USS Enterprise-C, which was destroyed in 2346 while defending a Klingon outpost from an attack by the Romulans. The action secured peace between the Federation and the Klingon Empire who saw this courageous sacrifice as a great act of Honor. The ship's destruction came some six months before it was due to return to Spacedock for modification.
The USS Ambassador was launched in 2330 and commissioned in 2332. Series production continued at a slow but steady pace until 2357, when the sixty eighth vessel was launched. Production was then suspended in favour of the new Galaxy class. As a class with a long and proven service history which had already had most of its flaws worked out decaids earlier a limited run of Ambassidor Class ships was made in the early 2360's to replace ships lost to attration among its own class and the Excelsior Class.
The Ambassador class would under take most of starfleets long range scientific and exploratory missions starting in the mid 2330s and would remian the premiere Starfleet Class until the Nebula and Galaxy Class ships started to come online in significant numbers in the late 2350s. Ambassador class ships would remain in front line service well into the 2370's and participated in almost every significant event in Starfleet during the 2360's and 2370's. Several ships of this class were lost at the Battle of Wolf 359 and in 2368 several ships would assist the Federation in revealing the Romulan involvement in the Klingon Civil War. A large number of Ambassador class ships were still in service when the Alliance broke down with the Klingons in 2372 and when the Dominion War started the following year. Having undergone several upgrades in the 2350s and 2360s the Ambassador Class of ships would still prove to be a capable design and would see action in nearly every major battle during that conflict.
At the end of the conflict the Excelsior Class and Miranda class ships were retired from active service. The remaining Ambassador Class ships would remain in service to supplement the new generation of Akira, Intrepid, Defiant and Sovergin class ships well into the late 2390s, undergoing several major upgrades and refits.