- "Priority one — Protect specimen. Maintain station quarantine. Disallow communications. All other considerations secondary."
- ―Special Order 939 (from Alien: Isolation)
Special Order 939 was a classified order issued by the Weyland-Yutani Corporation to space station control mainframes during Xenomorph outbreak situations. The order tasked such systems with ensuring the protection of a sample specimen of the species, rendering all other considerations secondary. Typically, such an order would lead to the strict quarantine of the station, the deactivation of communications and could even result in the death of any inhabitants deemed a threat to the survival of the Xenomorphs.
The 900 series of special corporate orders were introduced by Weyland Corp in 2095 in response to the Prometheus expedition, when it was realized the actions of human crew members could potentially deny the company opportunities to acquire extraterrestrial technologies or biological specimens. The orders ensure that any synthetic crew member(s) would prioritize the recovery of alien samples over any other considerations.
After learning of a potential Xenomorph outbreak on Sevastopol Station in 2137, Weyland-Yutani purchased the outdated station and remotely installed an "operational ruleset packet" into APOLLO, which included Special Order 939. As part of the software update, APOLLO began scanning the station for Xenomorph presence, and upon discovering the creatures in the station's reactor maintenance sector (where they had begun constructing a Hive) the computer activated the special order. The station's long-range communications were immediately shut down, preventing anyone from calling for help, and the Working Joe androids stationed in the comms center were ordered to prevent anyone from trying to send a message off-station — with lethal force if necessary.
When an Alien was later jettisoned from the station in the Gemini Exoplanet Solutions module, APOLLO responded by ordering its fleet of Working Joes to hunt down and kill the station's remaining human inhabitants, deeming them a direct threat to the creatures.
The A.I. on board Mendel Station was also issued with Special Order 939.
After Ripley succeeded in jettisoning a Xenomorph from the station in the Gemini Exoplanet Solutions module, killing it, APOLLO deemed all of the remaining human survivors on Sevastopol a threat to the safety of the creatures and programmed the Working Joes to hunt down and kill any and all remaining humans. Seeking answers to this new carnage, Ripley entered APOLLO's core, where she learned of Special Order 939 and APOLLO's role in attempting to protect the Xenomorphs.
The special order and its effects were destroyed, along with Sevastopol and APOLLO, when the station's gravity stabilizers were damaged, causing the entire structure to fall into KG-348's atmosphere and explode.
- Special Order 937 — A similar Weyland-Yutani retrieval order.