To keep these families safer during a battle, the Enterprise-D can separate its larger saucer section from its drive section, which is equipped with its own battle bridge. While the main bridge is located at the heart of the saucer section, the Enterprise-D's battle bridge is located on deck 8 of the secondary hull. The smaller bridge has all the same strategic functions as the main bridge, but does not have science or engineering stations. Additionally, the Enterprise-D's battle bridge only appears in three episodes of TNG, despite an impressive display of the ship's saucer separation in the series premiere.
3"Encounter At Farpoint"
Star Trek: The Next Generation Season 1, Episodes 1 & 2
As the newly-launched Enterprise-D travels to Deneb IV for its maiden voyage, the journey is interrupted by a god-like being known as Q (John de Lancie). Q goes on about humanity's violent history and easily thwarts all the crew's attempts to stop him. Trying to trick Q, Picard accelerates the Enterprise at high warp speeds, but Q maintains pursuit in the form of a ball of energy. As Q begins to gain on the Enterprise, Picard orders an emergency saucer separation at high warp, leaving Lt. Worf (Michael Dorn) in charge of the saucer section.
This way, most of the ship's crew and their families can flee in the saucer section, while the stardrive section turns to face Q. From the battle bridge, Picard sends out torpedoes to mask the departure of the saucer section. When the torpedoes have no effect, Picard has Troi (Marina Sirtis) send out a message of surrender. Q surrounds the stardrive section in a force field and transports the crewmembers aboard to a World War III-style courtroom.
The creators of TNG had plans to use the Enterprise-D's saucer separation more often, but the special effects required for the shots proved to be too expensive to use regularly.
Q then declares that all of humanity is being put on trial for being a "dangerous, savage child race." Picard suggests that Q test the Enterprise crew to see if humans are still savage, and Q agrees, saying that the upcoming Farpoint mission will determine humanity's fate. When the stardrive section arrives at Farpoint station, Commander William Riker (Jonathan Frakes) comes aboard and, on Picard's orders, expertly performs a manual docking of the two sections, successfully reconnecting the Enterprise.
2"The Arsenal Of Freedom"
Star Trek: The Next Generation Season 1, Episode 21
The Enterprise-D's battle bridge comes in handy again near the end of TNG season 1, when Lt. Geodi La Forge (LeVar Burton) is left in command of the ship. As the Enterprise approaches the planet Minos, they are greeted by a holographic recording of a salesman (Vincent Schiavelli) pitching a highly advanced weapons system. Riker, Data (Brent Spiner), and Yar (Denise Crosby) beam down to the planet to investigate and soon find themselves at the mercy of this weapons system.
After Riker becomes trapped within a static field of some kind, Captain Picard beams down to the planet with Dr. Beverly Crusher (Gates McFadden), leaving Geordi in command of the Enterprise. A cloaked automatic weapon soon attacks the Enterprise with increasingly powerful blasts that quickly weaken the ship's shields. The Chief Engineer of the week, Lt. Logan (Vyto Ruginis), insists that Geordi give him command, but Geordi mostly ignores him to focus on how to destroy the automated weapons. When the attack from Enterprise-D fails to hit the cloaked weapon, Geordi orders a saucer separation.
1"The Best Of Both Worlds, Part II"
Star Trek: The Next Generation Season 4, Episode 1
The final appearance of the battle bridge in TNG comes during the Enterprise-D's battle with the Borg cube in the excellent "The Best of Both Worlds" two-parter. In "Part I," the Borg kidnap Picard and assimilate him, turning him into their mouthpiece, Locutus. Having gained all of Picard's knowledge, the Borg easily thwart the Enterprise-D's initial attacks. The Borg cube then continues to Earth, with the damaged Enterprise unable to pursue. In command of the Enterprise, Riker continues chasing the Borg cube, implementing Lt. Commander Shelby's (Elizabeth Dennehy) plan to perform a saucer separation.
By the time the Enterprise arrives at Wolf 359, 39 of the 40 starships involved have been destroyed, with over 10,000 lives lost in what would become known as the Battle of Wolf 359.