This is a list of military terms and events used in the Evangelion franchise.
An A-801 Order was a code issued by the Japanese government (under the influence of SEELE) that removed legal protection and authority from NERV in The End of Evangelion. This allowed the Japanese government to have the military invade NERV HQ to "prevent" Third Impact (but they helped ironically cause this event).
It seems any order starting with "A" seems to be related to NERV and emergencies.
The expedition lead by Misato Katsuragi's father, Dr. Katsuragi, to the South Pole to research and experiment with Adam - the being that was found there. It was funded by SEELE to set in motion their plans. Resulted in Second Impact.
The goal of Operation US was to retrieve a cross-shaped satellite that had been launched into outer space, with Eva-01 inside of it. Evangelion Unit-02, having been partially repaired, was launched and connected to a massive booster array with Asuka as its pilot. Evangelion Unit-08 was also sortied, piloted by Mari but she was unable to gain sufficient enough altitude to do anything other than play a support role for Unit-02. After a successful launch for Unit-02, the Tesseract was acquired as a target. At this point Unit-02 was attacked by the Code 4A of the Nemesis Series. Unit-08 was able to snipe and destroy the units while Asuka secured the satellite. At this point, the Code 4B of the Nemesis Series was revealed to have been hiding on the tesseract, just as Unit-08 is forced to retreat. The Code 4B engaged Unit-02 with Field Reflection Coatings, and succeeded in removing one of the arms of Unit-02. Overwhelmed by the Code 4B, Asuka pleaded for Shinji to do something. Unit-01 unexpectedly awoke inside the satellite, and used a beam from its eyes to destroy the Code 4B.
Evangelion Units used
The Vatican Treaty (バチカン条約 Bachikan Jōyaku) is an international agreement in the Rebuild continuity allowing only three active Evangelion units per country. As a result, upon NERV HQ's reception of Evangelion Unit-03 from America for testing, Unit-02 is placed into containment under the jurisdiction of the IPEA, being the one of the three currently active Evas that technically remains under the control of Europe and not Japan.
Another term in the Vatican Treaty states that a country must not modify standard Evangelion Units for military purposes. This was mentioned by Ritzuko when she first encounters Eva 444B and Eva 4444C.
The treaty's ostensible reason for existing could be simple politics, in order to prevent any one country from amassing too many of the most potent weapon on Earth. However, given that a policy restricting Japan's access to Evangelions is wholly counterproductive in light of their position as the world's defense against the Angel threat, SEELE would probably have been able to pull some strings were there not a "deeper" reason for the three-Eva limit. One reasonable speculation that has been forwarded: four Evas active at any one place and time would risk recreating the conditions of Second Impact, by assembling the equivalent of four Adams.