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The bombing on June 21, 1941 of Fort Stevens in Oregon by the Japanese submarine 1-25 represented the first attack on a military installation in the United States during Second World War.

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The United States was targeted by German agents long before the country even entered the war. In the late 1930s, a clandestine spy ring consisting of 30 men and three women led by Frederick Duquesne gained access to key civilian posts in an effort to gather intelligence on American military activity and destabilize the country and its morale.

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The first shelling of the United States during the Second World War took place on February 23, 1941, when the Japanese submarine 1-17 attacked the Ellwood Oil Field, a large oil well and storage facility outside of Santa Barbara, California.

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Damage to the plant was minimal, but the implications of the bombardment were severe. The event sparked the West Coast invasion scare and influenced the decision to intern Japanese-Americans (pictured).

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The plot was foiled when George Dasch, one of the saboteurs from the New York group, chose to turn himself in to the FBI. The spy ring was quickly cracked, with all later found guilty and sentenced to death. President Franklin D. Roosevelt commuted Dasch's sentence to life in prison, together with another member of the team, Ernst Burger, who'd also chosen to betray his colleagues. Pictured is the July 1942 trial of the captured Germans.

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In June 1942, the Nazis again attempted to carry out an espionage mission on US soil. Eight German-born operatives, who were all naturalized American citizens, were tasked with sabotaging the American war effort by targeting key infrastructures and spreading panic, with two teams of four secretly dropped on Long Island and on Florida's coast.

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In one of the more bizarre military campaigns of the Second World War, Japan began launching waves of balloon bombs, or Fugos, against the United States from November 1944 to April 1945. These high altitude balloons were 'armed' with anti-personnel and incendiary explosives, triggered to drop after their extraordinary flight across the Pacific Ocean using the velocity of the jet stream to complete the 8,046-km (5,000 mi) deployment. Pictured is an aerial photograph of a balloon taken from a pursuing American plane.

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Against the odds, around 350 balloons made it across the Pacific, aimed at cities, forests, or farmlands. But they all proved largely ineffective as weapons due to damp forest conditions and malfunctions. However, one did find its mark, exploding over Oregon and causing six civilian deaths. Pictured is a captured balloon, reinflated by US Army personnel.

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The military strike on Pearl Harbor by the Imperial Japanese Navy Air Service was carried out for a myriad of reasons, including the US's interference in the war between Japan and China. Ultimately, the attack led to America declaring war on Japan.

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In early June 1942, the only two invasions of the United States during the war of a US incorporated territory occurred when Japanese forces occupied Attu and Kiska in the Aleutian Islands, belonging to the state of Alaska. The incursion prompted the Aleutian Islands campaign, a response by America to retake the islands. American units are pictured making landfall in the region.

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Japan seizing American soil was a huge blow to morale. But by May 1943, the stars and stripes was once again being flown over the two remote and sparsely inhabited islands. It's believed Japan carried out the attack either to divert US forces away from the Battle of Midway, or as a means of preventing America launching an invasion of Japan from the Aleutians.

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In two attacks on September 5 and November 2, 1942, German U-boats targeted the anchorage for bulk carriers shipping iron ore on Bell Island (pictured) in Newfoundland and Labrador. Four ships were sunk and 70 merchant mariners lost their lives. During the encounter, an errant torpedo struck a loading bay on shore—the only location in North America to be subject to direct attack by German forces during the global conflict.

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One of the submarines involved in the Bell Island attack was U-518. The vessel was in fact on its way to rendezvous with a German patrol off the Gaspé Peninsula where it landed a Nazi spy, Werner von Janowski (pictured). He was captured by the Royal Canadian Mounted Police before he could reach Montreal. He was subsequently jailed in England for the duration of the war.

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The Battle of the St. Lawrence was an extension of the larger Battle of the Atlantic. Taking place from May–October 1942, September 1943, and again in October–November 1944, the several near-shore actions that took place during this period would mark the first time that a foreign power had inflicted casualties in Canadian inland waters since the US incursions in the War of 1812. The battle effectively began on May 12, 1942 when the German submarine U-553 torpedoed and sank the British freighter Nicoya at the mouth of the St. Lawrence River, not far from Anticosti Island in Quebec.

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Hours later, U-553 struck again in the same vicinity near Anticosti Island (pictured in the 1940s), this time sinking the Dutch freighter Leto.

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In September, U-91 caught up with HMCS Ottawa, sinking her with two torpedoes. The following month the Newfoundland Railway passenger ferry SS Caribou was torpedoed in the Cabot Strait by U-69, with heavy loss of life.

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In late October 1944 U-1223 entered the Gulf of St. Lawrence undetected and attacked and sunk the Canadian freighter SS Fort Thompson.

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Success by the Royal Canadian Navy throughout much of 1943 in foiling U-boat attacks led to the reopening in early 1944 of shipping lanes in the Gulf of St. Lawrence and St. Lawrence River to domestic and war-related convoys. But that saw a resurgence of U-boat activity.

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Three weeks later, the same vessel snuck up on HMCS Shawinigan. A single torpedo doomed the corvette to a watery grave with the loss of all hands.

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Axis losses were also high. Pictured is the funeral at Hampton National Cemetery in Virginia for 29 German crewman from U-85.

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Thousands were killed across Torpedo Alley, many of whom were civilians and merchant mariners. The last sinking of a German submarine was that of U-701, attacked on July 9, 1942. Pictured are survivors being picked up by a Coast Guard PH-2 seaplane.

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Pictured: German survivors from U-701 being brought ashore at Naval Station Norfolk, in Virginia, by US Navy personnel.

Sources: (FBI) (Smithsonian Magazine) (History) (NPR)

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Despite early successes, the secret cell was toppled after one of its members, a man called William G. Sebold, became a double agent for the FBI. The Feds arrested Duquesne and all 32 of his operatives in the biggest espionage bust in American history. On December 13, 1941—just days after the attack on Pearl Harbor—all were convicted and sentenced to serve a total of over 300 years in prison. Pictured is double agent Sebold (left) talking to Duquesne in Sebold's bogus office in Manhattan. The conversation was captured on surveillance tape through a two-way mirror.

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The submarine responsible, 1-25, would again make history during what became known as the Look Out Air Raids. The sub returned to the Oregon coast in September, and from its deck a seaplane was launched. The aircraft proceeded to drop two incendiary bombs over woodland with the intent of starting a forest fire. Thanks to light winds and a quick response from fire patrols, the bombing run inflicted only minor damage. The attack was the first time the mainland United States was bombed by an enemy aircraft.

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The attacks on the SS Fort Thompson and HMCS Shawinigan marked the end of the Battle of the St. Lawrence. German U-boats began surrendering to Canadian forces while others were shown little mercy by Allied warships and aircraft.

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The loss of HMCS Shawinigan was the worst case of military deaths in Canadian territory during the war. In total, 91 crew members lost their lives.

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Besides Canada, the Atlantic Theater also saw the east coast of the United States stalked by German U-boats. In fact, throughout 1942 the area surrounding the Outer Banks, including Cape Lookout and Cape Hatteras, in North Carolina became known as "Torpedo Alley" for the almost 400 ships sunk along this stretch of coastline. Pictured is the Dixie Arrow ablaze off Cape Hatteras on March 24, 1942 after being attacked by U-71.

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On December 7, 1941, Japan attacked Pearl Harbor, a US naval base near Honolulu, Hawaii. At the time, the United States was a neutral country and not engaged in the Second World War.

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The summer of 1942 proved productive for the German Kriegsmarine. In late August, two U-boats made a joint raid on the St. Lawrence. U-517 sank nine ships and damaged another in a two-week period.

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When talking about enemy attacks on US soil during the Second World War, most people refer to the bombing of Pearl Harbor. The infamous military strike by the Imperial Japanese Navy ultimately led to America declaring war on Japan. But even before those dark events of December 7, 1941, the country was being infiltrated by German spies. Bombardments and incursions by Axis forces on and into North American territory followed. But few people are able to recall these small-scale campaigns that saw the enemy directly target the nation and in some cases actually operate within American and Canadian borders. So, what are these little-known encounters, and when did they take place?

Click through and discover all about when World War II visited North America.