Ship class
A ship class was a shared construction design of spacecraft or starship operated by an entity. 

Large research and testing efforts went into perfecting a new ship class before construction, such as the Galaxy Class Starship Development Project by Starfleet or the development process of the D7 class by the Klingon Empire. (, )

Starfleet's primary hub of ship class research and development was Utopia Planitia Fleet Yards on Mars. (, )

In 2365, Geordi La Forge implemented a change to the design of the dilithium crystal orientation aboard the . Upon viewing the modification, one of the ship's designers, Leah Brahms observed that his modification was due to be introduced in the next class starship. ()

Starfleet often continued the Earth tradition of naming the first starship of a class after the class, such as the , the first  starship launched, or the , the first  starship launched. These vessels often bote the registry prefix NX. Starfleet also commonly continued the tradition of listing a starship's class on it's dedication plaque. (; )

The term sister ship was often used to describe vessels of shared lineage. (, et al.) 
By 2267, at least twelve  commissioned by Starfleet. ()

Some Klingon ship classes used a "D" prefix before a number (i.e. D4 class, D5 class, D7 class, or D12 class.) (; )

In the late 24th century, the  starship was often the point of comparison for ship classes. The Duras sisters admitted that their Bird-of-Prey was "no match" for a Galaxy-class starship. In 2371, Admiral Patterson described the  as "not as big as a Galaxy-class, but she's quick and smart..." (, )

Appendices

See also
Starship classes
Starship classes (alternate reality)

Background information
Shared ship classes has had the added benefit to Star Trek of reducing production costs and production time when a new ship is needed, especially in the age of studio models.

The Star Trek: The Next Generation Technical Manual portrays a twenty-year design and construction process of Galaxy-class ships, although  and  seem to suggest that this timeline was much faster. The , launched in 2371, was said to be developed in response to the Borg which first presented themselves as a threat in 2365/2366.

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