World War II's longest continuous campaign takes place, with the Allies striking a naval blockade against Germany and igniting a struggle for control of Atlantic Ocean sea routes. The Axis, with its U-boats, responds with a counter-blockade that is at first successful, but the Allies' use of convoys, aircraft and technology eventually turns the tide. Over five years, thousands of ships engage in 100-plus battles in the Atlantic Ocean with approximately 100,000 lives lost.

A German invasion around the French coastal town of Dunkirk separates the French and British armies, marooning Allied forces. But with Adolf Hitler halting Germany's advance there, the Allies are able to perform a daring—and successful—evacuation, called Operation Dynamo. Germany claims victory with remaining Allied troops surrendering, but the evacuation serves to boost British morale, still referred to as the "Dunkirk spirit."

After a nearly four-month air campaign waged over England, Britain's Royal Air Force and Navy respond to heavy bombing attacks from Germany's Luftwaffe air force, including “the Blitz,” in an attempt to destroy the RAF before invading. Defense systems, including radar, and Hitler's decision to bomb London, rather than military bases, allows Britain to regroup and eventually win the battle.

Nazi paratroopers invade the Greek island of Crete, marking history's first mostly airborne attack. Day one of the campaign results in heavy losses for the Germans, but fearing a sea assault, Allied forces soon withdraw and evacuate in defeat. With nearly 4,000 Allies and more than 3,000 Germans killed, however, Hitler decries "the day of the parachutist is over" and it is the country's last airborne campaign.

German and Finnish soldiers begin a nearly 900-day siege and blockade of Leningrad (now St. Petersburg), the second-biggest Soviet city and a major center of industry. With supplies, water, electricity and transportation cut off, 1.3 million people are evacuated. As the Red Army finally begins to break through the blockade, the siege ends and the city is freed, but approximately 800,000 civilians die, most from hunger.

Following Germany's Operation Barbarossa, an invasion of the Soviet Union, the Axis launches a campaign to capture the capital city of Moscow before winter sets in. In preparation, the Soviets fortify the city and bring in reinforcements. After a series of gains and losses on both sides during harsh weather, the Germans are eventually beaten back and forced to retreat.

In a surprise wave of attacks on the U.S. naval base at Oahu Island, Hawaii's Pearl Harbor, Japan, aligned with the Axis, takes out America's Pacific fleet (the fleet's three aircraft carriers are not present during the attack). With approximately 2,400 U.S. troops killed and another 1,000 wounded, President Franklin D. Roosevelt calls it "a date which will live in infamy" and, the next day, the U.S. officially enters World War II, declaring war on Japan.

In a counter-offensive after Germany's attack on Moscow, the Soviet Red Army attacks Kharkov, Ukraine with the aid of 1,500 tanks and 1,000 aircraft but German intelligence alerts the Axis to the campaign. Facing nearly 300,000 casualties and gaining little traction, the Soviets are forced to concede.

In one of America's most important World War II naval wins, American intelligence is able to break codes to thwart a Japanese attack on the US. at Midway Island in the Pacific Ocean. With Japan focused on Midway, U.S. forces, including dive bombers, attack, sinking four of Japan's aircraft carriers and the victory serves as a turning point in the conflict.

Weeks after Japan begins building a strategic airfield on Guadalcanal, part of the Solomon Islands in the South Pacific Ocean, U.S. forces launch a surprise attack, taking control of the airfield and forcing the Japanese into initial retreat. But with reinforcements arriving, hand-to-hand jungle combat follows with Japan finally retreating six months later, with 31,000 casualties and the loss of 38 ships. The Allies lose 29 ships and 7,100 soldiers.

In a conflict that marks the war's outcome tipping in the favor of the Allies, the Red Army defends the Russian city of Stalingrad from German attack, bringing an end to the Axis's eastern Europe advances and handing it its first decisive defeat. One of the longest, biggest and deadliest battles of the war, it ends with close to 2 million casualties, including civilians, with brutal winter weather and a Russian blockade causing many Germans to starve to death.

The Allies invade French North Africa in an attempt to draw the Axis away from Soviet attacks on the Eastern Front and gain control of the Mediterranean shipping lanes. Gen. Dwight D. Eisenhower leads attacks on Oran, Algiers and Casablanca before advancing on Tunis and causing the Vichy French to realign with the Allies. The victory is touted by Winston Churchill as the "end of the beginning."

Military history's largest tank battle takes place on the Eastern Front involving an estimated 6,000 tanks, 4,000 aircraft and 2 million soldiers. In its last blitzkrieg offensive, Germany attacks the Red Army near Kursk, Russia, but due to delays and the cracking of the German Wehrmacht code, the Soviets are prepared and keep Hitler from conquering Russia.

Advancing in Italy toward Rome, the Allies attack the Gustav Line, held by the Axis, at the mountain town of Monte Cassino, home to a Benedictine abbey dating to 524 A.D. Evacuated by the Germans, both sides tell the Vatican it will not be attacked or used in military operations. However, in a bomber attack by the Allies, the abbey is destroyed, leading to public outcry and, post-bombing, as shelter for the Nazis. Polish troops capture the abbey on May 18, leading the way for the Allied capture of Rome soon after.

Attempting to liberate Italy, the Allies land at Anzio, catching the Germans by surprise and quickly securing a beachhead during Operation Shingle. However, continued Axis resistance and counter-attacks ensue, resulting in a stalemate that doesn't end until the fall of Rome. It’s seen as a failure for the Allies, although it does keep German troops from moving to France in the days before the invasion at Normandy.

Japan attacks Allied forces who have advanced in the Pacific Theater to the Marianas Islands in the war's largest aircraft carrier battle. Prepared for the strike, the United States launches a stunning counter-attack, and the battle is later called the "Marianas Turkey Shoot" due to minimal U.S. casualties and the Japanese losing some 600 aircraft, two oilers and three carriers.

American, British and Canadian troops storm five beaches at Normandy France June 6, known as D-Day, waging one of military history's largest water invasions. At Omaha Beach, more than 2,000 American casualties are suffered with some 4,000 deaths that day. But by June 11, the beaches are secured and 325,000-plus forces have landed. The Allies begin their advance across Normandy, eventually liberating Paris.

In World War II's largest naval battle, the Allies invade the Philippines to retake the commonwealth and create a Southeast Asian blockade. In a counter-attack, Japan deploys its first kamikaze, or suicide, bombers. Despite heavy U.S. casualties—more than 23,000 U.S. soldiers and sailors are killed—Japan suffers nearly 420,000 casualties and the conflict serves to cripple most of Japan's surface fleet, giving the Allies command of the Pacific.

Fought in brutal, frigid winter conditions, Hitler's forces launch a surprise, last-ditch counter-attack in an attempt to split the line of the Allies on the Western Front at the forested region of Ardennes in Belgium and Luxembourg. The battle becomes known as Battle of the Bulge, because the Germans created a “bulge” around the area of the Ardennes forest in pushing through the American defensive line.

After early German success, the Allies regain their positions thanks, in part, to reinforcements and an eventual Christmas Day airstrike once the weather clears. The Allies win (German casualties number 100,000-plus and American casualties are estimated to be 81,000) and continue their advance toward Berlin.

Fought 660 miles south of Tokyo, U.S. Marines invade the volcanic island of Iwo Jima seeking a strategic staging area for a possible attack on Japan's mainland. Weeks of bloody battle follow and while the Americans eventually gain control, 7,000 Marines are killed, with 20,000 wounded. All but 216 of 18,000 Japanese soldiers are killed. The island later serves as an emergency landing sight for B-29 bombers.

Soviet forces, with support from American and British aircraft, launch an offensive against the German capital of Berlin in one of World War II's final major battles. As the Red Army encircles the city, capturing Gestapo headquarters, Hilter commits suicide April 30 in the Führerbunker and Germany surrenders a few days later, essentially ending the war.

World War II's final major battle—and one of the war's bloodiest—begins Easter Sunday as U.S. Army and Marine forces invade Okinawa in the Ryukyus island chain southwest of Japan with the orders of taking the island to execute air strikes against Japan and create a blockade.

Counter-striking with kamikaze attacks, the Japanese sink 26 Allied ships and damage nearly 170 more, causing more than 12,000 American deaths over the three-month battle. Finally overpowered by the Americans, many surviving Japanese kill themselves rather than surrender. In the end, more than 100,000 Japanese are killed, along with 150,000 civilians.