The Daedalus class was one of Starfleet's earliest designs, in service in the 22nd century, with a spherical forward hull and a cylindrical secondary hull, and included the lost USS Essex.
The class is named in the Next Generation episode Power Play, in which the Enterprise-D picks up an old distress call from the USS Essex. Data identifies the ship as Daedalus class and notes that it was lost more than two centuries earlier and that the type was withdrawn from service in 2196.
No ship of the class is shown in flight. The design is known from a model, built from an early concept by Matt Jefferies for the original Enterprise, which sits in Sisko's office in Deep Space Nine among other historic ships.
Reference works also assign the USS Horizon and the USS Archon of the original series to the class, though neither is identified that way in dialogue.