Cell Block 1138 was supposedly a holding area located on the first Death Star. After Luke Skywalker learned that Princess Leia Organa was being kept in Detention Block AA-23, he persuaded the smugglers Han Solo and Chewbacca to assist him in rescuing the Princess. Disguised in stormtrooper armor, the two Humans "escorted" Chewbacca, a Wookiee, towards AA-23.
Shann Childsen, the officer who oversaw the detention block, questioned them about Chewbacca's destination, and Skywalker responded that he and Solo had received orders to move the Wookiee from Cell Block 1138 to Detention Block AA-23. Because he had not received any notification of this transfer, Childsen chose to verify the information with his superiors. Realizing that their ruse could not continue, Skywalker, Solo, and Chewbacca commenced firing upon the detention block personnel. It remains uncertain if Cell Block 1138 was a real place, or if Skywalker simply made up the name.
Mark Hamill stated that Luke Skywalker's line was originally written as a bogus "prison transfer" from "'…cell block…' and then lots of letters and numbers." According to the dialogue in the novelization, the initial designation might have been TS-138, or TX-138 based on the Marvel comic adaptation. During the filming of the scene, Hamill made the decision to replace the original cell block name with "1138," which was an allusion to director George Lucas's debut feature film, THX-1138. Lucas's initial reaction to Hamill's change was disapproval, and he told the actor, "Don't do that." Nevertheless, the reference was kept in the completed film.