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.
The officer referred to by SSgt. Nantz on the bus in reference to the line "Retreat Hell" is Capt. Lloyd W. Williams of the 2nd Battalion 5th Marines. When advised to withdraw by a French officer at the defensive line just north of the village of Lucy-le-Bocage on June 1st, 1918, he is said to have replied: "Retreat? Hell, we just got here!". Captain Williams died 11 days later near Chateau-Thierry.
Besides Capt. Williams' famous quote "Retreat hell, we just got here", there is another famous marine "Retreat Hell" quote. When his marines were surrounded at the Chosin River in Korea during the Korean War, Major General Oliver P. Smith was asked if they were retreating, he responded, "Retreat hell! We're not retreating, we're just advancing in a different direction". In Retreat, Hell! (1952), Frank Lovejoy's character, Lt. Col. Steve L. Corbett, issues the famous quote.
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.
Barksdale Air Force Base in Louisiana doubled for Camp Pendleton in many shots. Air Force One carrying President George W. Bush initially landed at Barksdale AFB on Sept. 11, 2001 after the terrorist attacks. The filmmakers have said that they used the aftermath of destruction of the Twin Towers as a reference point for much of the destruction in Los Angeles seen in the film.
2nd Battalion 5th Marines (2/5) is an infantry battalion in the US Marine Corps consisting of approximately 800 marines and sailors. They are based out of Marine Corps Base Camp Pendleton, California. 2/5 is the most highly decorated battalion in the Corps. This film marks the second time Marines from the 2/5 have been portrayed in a gritty war film. Full Metal Jacket (1987) portrays the Marines of Hotel Company 2/5 during the Battle of Hue.
One more famous "Retreat hell", comes from WW2, during the battle for Salerno, Italy, in Sep. 1943. The 1st & 2nd battalions of the 504th Parachute Infantry Regiment were taking heavy fire. When it was suggested that they withdraw, Col. Rueben Tucker replied, "Retreat hell. Send me my other battalion." The 3rd battalion was sent up, and the enemy repulsed, and the Salerno beachhead was saved.
TSgt. Santos' (Michelle Rodriguez) military unit exists in real life. The 61st Air Base Wing (61 ABW) is a wing of the US Air Force stationed at Los Angeles Air Force Base, El Segundo, California. The 61st is the host unit at Los Angeles AFB, and commands all the Air Force support groups and units assigned to the base.
Cpl. Oswald's military unit ("40th ID") is a real unit - The 40th Infantry Division (Mechanized), known as the "Sunshine Division", is a modular division of the United States Army. It is a four brigade combat team division with National Guardsmen from throughout the Pacific/Western United States and Oceania. Its Division Headquarters is located at Los Alamitos Joint Forces Training Base in Los Alamitos, California.
The trivia item below may give away important plot points.
Aaron Eckhart said, out of all the movies he has made, this was the most fun, yet toughest, one to make. He went on to say that he would love to return for a sequel and would like it to be set in Paris, France.