Death Star
The Death Star is a type of fictional mobile space station and galactic superweapon featured in the "Star Wars" space opera franchise. The first Death Star is stated to be more than 100 km to 160 km in diameter, depending on source. It is crewed by an estimated 1.7 million military personnel and 400,000 droids. The second Death Star is significantly larger, between 160 km to 900 km in diameter depending on source, and technologically more powerful than its predecessor. Both versions of these moon-sized fortresses are designed for massive power-projection capabilities, capable of destroying multiple naval fleets or entire planets with one blast from their superlasers.
Rebel Alliance
During the events of "Rogue One" and "A New Hope", the Alliance learns of the construction of the "Death Star", an enormous battle station intended to secure the Empire's power. With the help of the "Rogue One" squad led by Jyn Erso and Cassian Andor, the Rebels successfully steal the schematics of the station. This win was the Alliance's first major battle against the Empire on Scarif; but at a 75% casualty rate and with all remaining imperial and rebel forces planetside decimated. After successfully downloading the Death Star plans, Alderaanian soldiers aboard a Mon Calamari flagship barely manage to escape Imperial forces with the stolen data plans. Right after the battle, the "Tantive IV", an Alderaanian corvette carrying Princess Leia Organa is captured by the Imperial fleet while attempting to deliver the Death Star Plans to Bail Organa on Alderaan. All members of the Alderaanian Consular Security onboard are either killed or taken prisoner and Princess Leia Organa is held hostage for a time by Darth Vader. In order to punish both her and her home planet's central involvement in the Rebel Alliance, Leia is forced to witness Alderaan's destruction by the Death Star. The Princess is subsequently rescued by Luke Skywalker, Han Solo, Chewbacca, and Obi-Wan Kenobi, who then deliver the station schematics to the Alliance. This leads directly to the Alliance's victory in the Battle of Yavin and the loyalty of Luke Skywalker; the Rebellion's only remaining member with training in the Force.