Very little of the film was actually shot in Los Angeles. Tax incentives brought the production to Louisiana where sets of Los Angeles streets were constructed.
The film is inspired by the real-life incident known as the Battle of Los Angeles, during World War II. On the night of 24-25 February 1942, unidentified aircraft were allegedly spotted in the airspace above Los Angeles. Suspecting it to be the Japanese, a blackout of the city was ordered and over 1,440 rounds of anti-aircraft ammunition was fired. Upon finding no evidence of the existence of any enemy aircraft, the incident was declared to be a "false alarm". The event has since been chalked up as a result of "war nerves", likely triggered by a lost weather balloon and exacerbated by stray flares and shell bursts from adjoining anti-aircraft batteries.
Marines from Camp Pendleton helped train the actors for their roles, educating them in the Marine lifestyle. A number of actual marines also appear as extras in the film. To thank them, a sneak preview of the film was shown at Camp Pendleton on March 3rd, 2011.
When Nantz uses a Thales PRC 148 MBTIR to attract the alien probe into a gas station, the radio's display is blank indicating it is either a dummy prop or not switched on.
The first utility vehicle SSGT Nantz fired the .50 cal from showed a close up of a spent cartridge which fell from the gun and it showed the crimp marks of a blank and not the perfect round shape of a spent .50 cal ball round.
In the early scenes set in Camp Pendleton, several A-10's are shown on the flight line. A-10's are flown exclusively by the U.S. Air Force, not the Marines. MCAS Camp Pendleton houses only helicopter squadrons, and fixed wing close air support aircraft such as F/A-18's and AV-8B Harriers would be launched from other nearby Marine bases such as Miramar.