The JANUS Class
Named for the ancient Roman Two-Headed God of Beginnings and Endings, the Janus Class starship was first designed in late 2269, in response to issues raised following several Galaxy-Class saucer separations. It was determined that while the Galaxy-Class saucers were adequate for the purpose of serving as a nonessential crew haven while the Stardrive section engaged in combat, their effectiveness was limited by their lack of warp power, making a quick getaway or battle maneuvers nearly impossible, should the Stardrive happen to come to grief or be otherwise disabled. The thought of an entire crew attempting to limp home on impulse power from a deep-space exploratory mission was unpalatable, at best. Thusly, the Janus was designed to counteract that eventuality. With two independent warp systems, the Janus is also capable of a wider variety of combat options, a feature put to further use in the development of the Prometheus-Class some years later.
"Offering Dragons quarter is no good, they regrow all their parts and come on again. They have to be killed." -- John Berryman
JANUS Saucer Section
The Saucer section has two fold-out nacelles, reminiscent of the fold-out landing gear on ancient aeroplanes. These engines form a close warp field around the saucer, adding to its mobility at high speeds. They are not operated while the vessel is combined, although it is theorized that they would be enough to propel the entire vessel at low warp, should it prove necessary. Although the original design called for jettisonable hull plates (which might later have proved a hazard to navigation, and which certainly would have required stays at a starbase to replace,) to cover the engines, advances in technology rendered that concept obsolete.
JANUS Stardrive section.
As on a Galaxy-Class starship, the Stardrive is fully capable of independent operation, with its own fully equipped battle bridge and other facilities. As well, additional phasers and other weapons are made available once the Saucer section is removed.