The engineering section is a common feature of Federation starships. It is a large, cylindrical section of the ship that usually houses the ship's engineering areas, separating them from the ship's bridge and crew quarters, which are usually housed in a disc-shaped hull component. The engineering section is often connected to the ship's warp nacelles by additional struts. Federation ships that do not have an engineering hull usually have an expanded section of their saucers that serves this purpose and/or a 'roll-bar' structure that holds the systems usually contained in this section.
The engineering section typically has an auxiliary bridge which can be used to control the ship if the main bridge is damaged or inaccessible. For unspecified reasons, the controls in the auxiliary bridge can often override those of the main bridge.
The engineering section of a Galaxy-class starship is often described as the secondary hull (with the saucer section referred to as the "primary hull"). In this class, the engineering section can separate from the saucer section and operate independently, albeit with somewhat less power, since the saucer section has impulse engines that will not be available while the ship is separated.