Mainland invasion of the United States
The concept of a mainland invasion of the United States relates to military theory and doctrine which address the feasibility and practicality of a foreign power attacking and successfully invading the continental United States of America.
The military history of the United States began with a foreign power on U.S. soil, the British Army during the American Revolutionary War. Following American independence, the next occurrence of an attack on American soil was during the War of 1812, also with Britain, and also the first and only time since the end of the Revolutionary War in which a foreign power occupied the American capital (the then capital city of Philadelphia was also occupied by the British during the Revolution).
The American Civil War may be seen as an invasion of home territory to some extent, with both the Confederate and Union armies each making forays into the other side's home territory. After the Civil War, the threat of an invasion from a foreign power was small, and it was not until the 20th century that any real military strategy was developed to address the possibility of an attack on America.
Although not by a foreign nation, on March 9, 1916, Mexican revolutionary Pancho Villa and his Villistas invaded Columbus, New Mexico in the Border War’s Battle of Columbus, triggering the Pancho Villa Expedition in response, led by Major General John J. Pershing.
Until the year 1935, the greatest potential threat to attack the United States was seen as the British Empire. To that end, military strategy was developed to not only forestall a British attack, but also attack and occupy Canada. "War Plan Red" was specifically designed to deal with a British attack on the United States and a subsequent invasion of Canada. Similar plans existed for a 20th-century war with Mexico, although the ability of the Mexican Army to attack and occupy American soil was considered negligible, as demonstrated by the Mexican reluctance to accept the provisions of the Zimmermann Telegram.
On the opposite side of the Atlantic, the Imperial German Navy maintained a battle plan to engage the United States Atlantic Fleet off Norfolk, Virginia, followed by shore bombardment of eastern cities. The actual feasibility of such an attack is questionable, and the idea of a naval invasion of the U.S. was more tied to the foreign policy of Kaiser Wilhelm II, rather than practical military design.
World War II
During World War II, the defense of the mainland United States was considered part of the American theater. The American Campaign Medal was awarded to military personnel who served in the United States in official military duties.
When war was declared between Germany and the U.S. in 1941, the German High Command immediately recognized that current German military strength would be unable to attack or invade the United States directly. Military strategy instead focused on submarine warfare, with U-boats striking American shipping in an expanded Battle of the Atlantic, particularly an all out assault on U.S. merchant shipping during Operation Drumbeat.
Adolf Hitler dismissed the threat of America, stating that the country had no racial purity and thus no fighting strength, further quoted that "The American public is made up of Jews and niggers". German military and economic leaders had far more realistic views, with some such as Albert Speer recognizing the enormous productive capacity of America's factories as well as the rich food supplies which could be harvested from the American heartland.
In 1942, German military leaders did briefly investigate and consider the possibility of a cross Atlantic attack against the U.S. — most cogently expressed with the RLM's Amerika Bomber trans-Atlantic range bomber design competition, first issued in the spring of 1942 — proceeded forward with only five airworthy prototype aircraft created between two of the competitors, but this plan had to be abandoned due to both the lack of staging bases in the Western Hemisphere, and Germany's own rapidly decreasing capacity to produce such aircraft as the war wore on. Thereafter, Germany's greatest hope of an attack on America was to wait to see the result of that nation's war with Japan. By 1944, with U-Boat losses soaring and with the occupation of Greenland and Iceland, it was clear to the German military leaders that the dwindling German armed forces had no further hope to attack the United States directly. In the end, German military strategy was in fact geared toward surrendering to America, with many of the Eastern Front battles fought solely for the purpose of escaping the advance of the Red Army and surrendering instead to the Western Allies.
One of the only officially recognized landings of German soldiers on American soil was during Operation Pastorius, in which eight German sabotage agents were landed in the United States (one team landed in New York, the other in Florida) by U-Boats. The team was quickly captured and put on trial as spies, rather than prisoners-of-war, due to the nature of their assignment. After the court found them guilty of espionage, six German agents were executed in the electric chair at the Washington D.C. jail. The other two were not put to death and instead received prison terms because they willingly turned on their comrades by defecting to the United States and told the FBI about the mission's plan. In 1948, three years after World War II ended, the two were freed and returned to Germany.
The feasibility of an attack on the United States by Imperial Japan was considered negligible, with Japan possessing neither the manpower or logistical ability to successfully mount a full-scale invasion of the U.S. Minoru Genda of the Imperial Japanese Navy advocated invading Hawaii after attacking Pearl Harbor, believing that his country could use Hawaii as a base to threaten the mainland United States, and perhaps as a negotiating tool for ending the war. The American public in the first months after the attack on Pearl Harbor feared a Japanese landing in California and reacted with alarm to a rumored raid in the Battle of Los Angeles.
During the war, Japan successfully occupied, but later withdrew from, the Aleutian Islands of Alaska. Japan also conducted air attacks through the use of fire balloons. Six American civilians were killed in such attacks; Japan also launched two manned air attacks on Oregon (the only time in the war that mainland America was bombed by enemy aircraft) as well as two incidents of Japanese submarines shelling the American mainland.
During the Cold War, the primary threat of an attack on the United States was viewed to be from the Soviet Union. In such an attack, nuclear warfare was projected to almost certainly happen, mainly in the form of Intercontinental ballistic missile attacks as well as Soviet Navy launches of SLBMs at U.S. coastal cities,
The first Cold War strategy against a Soviet attack on the United States was developed in 1948, made into even firmer policy after the Soviet development of the atom bomb in 1949. By 1950, the United States had developed a defense plan to repel a Soviet nuclear bomber force through the use of interceptors and anti-aircraft missiles, while at the same time launching its own bomber fleet into Soviet airspace from bases in Alaska and Europe. By the end of the 1950s, both Soviet and U.S. strategy included nuclear submarines and long range nuclear missiles, both of which could strike in as little as ten to thirty minutes while bomber forces took as long as four to six hours to reach their targets. The concept thus developed of the nuclear triad where all three weapons platforms (land based, submarine, and bomber) would be coordinated in unison for a devastating first strike, followed by a counterstrike, accompanied by "mopping up" missions of nuclear bombers.
American nuclear warfare planning was nearly put to the test during the Cuban Missile Crisis. The subsequent blockade of Cuba also added a fourth element into American nuclear strategy, this being surface ships and the possibility of low yield nuclear attacks against deployed fleets. Indeed, the United States had already tested the feasibility of nuclear attacks on ships under Operation Crossroads. Reportedly, during the Cuban missile crisis, one Soviet submarine nearly launched a nuclear torpedo at an American warship, yet the three officers required to initiate the launch (the Captain, Executive Officer Vasili Arkhipov, and the Political Officer) could not agree to do so. By the 1970s, the concept of mutually assured destruction led to an American nuclear strategy which would remain relatively consistent until the end of the Cold War.
In the theater of 21st century warfare, United States strategic planners have been forced to contend with various threats to the United States ranging from direct attack, terrorism, as well as unconventional warfare such as a cyber war or economic attack on American investments and financial stability.
Several modern-day armies operate nuclear weapons with ranges in the thousands of kilometers. Mainland U.S. is therefore vulnerable to nuclear attack by powers such as the United Kingdom, Russia, China, France, and Israel.
The top U.S. military command overseeing the defense of the continental United States is the United States Northern Command.
The threat of a terrorist attack on the United States was made clear during the 1993 World Trade Center bombing and the 9/11 hijacking attacks on the World Trade Center in New York City and the Pentagon in Washington DC. Since that time, the Department of Homeland Security has been the primary agency to deal with terrorist attack threats towards the United States.
Cyber and economic attacks
The risk of cyber-attacks on both civilian and military computer targets was brought to light after China became suspected of using government funded hackers to disrupt American banking systems, defense industries, telecommunication systems, power grids, utility controls, air traffic and train traffic control systems, as well as certain military systems such as C4ISR, and ballistic missile launch systems.
Attacks on the US economy, such as efforts to devalue the dollar or corner trade markets to isolate the United States is currently considered another method by which a foreign power may seek to attack the United States.
In popular culture
A number of films and other related media have dealt with fictitious portrayals of an attack against the United States by a foreign power. One of the more well known films is Red Dawn, detailing an attack against the U.S. by the Soviet Union, Cuba, and Nicaragua, with the film remade in 2012 detailing a similar attack launched by North Korea and Russia. Other U.S. invasion films include Invasion U.S.A., Olympus Has Fallen, and White House Down, as well as The Day After and By Dawn's Early Light, both of which detail nuclear war between US and Soviet forces.
A terrorist occupation of Washington, D.C. was the subject of a G.I. Joe cartoon episode, when Serpentor led Cobra forces to occupy the American capitol. A terrorist occupation of the capital was also seen in G.I. Joe: Retaliation.
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