On this day in 1942, the U.S. 1st Marine Division begins Operation Watchtower, the first U.S. offensive of the war, by landing on Guadalcanal, one of the Solomon Islands.

On July 6, 1942, the Japanese landed on Guadalcanal Island and began constructing an airfield there. Operation Watchtower was the codename for the U.S. plan to invade Guadalcanal and the surrounding islands. During the attack, American troops landed on five islands within the Solomon chain. Although the invasion came as a complete surprise to the Japanese (bad weather had grounded their scouting aircraft), the landings on Florida, Tulagi, Gavutu, and Tananbogo met much initial opposition from the Japanese defenders.

But the Americans who landed on Guadalcanal met little resistance-at least at first. More than 11,000 Marines had landed, and 24 hours had passed, before the Japanese manning the garrison there knew of the attack. The U.S. forces quickly took their main objective, the airfield, and the outnumbered Japanese troops retreated, but not for long. Reinforcements were brought in, and fierce hand-to-hand jungle fighting ensued. "I have never heard or read of this kind of fighting," wrote one American major general on the scene. "These people refuse to surrender."

The Americans were at a particular disadvantage, being assaulted from both the sea and air. But the U.S. Navy was able to reinforce its troops to a greater extent, and by February 1943, the Japanese had retreated on secret orders of their emperor (so secret, the Americans did not even know it had taken place until they began happening upon abandoned positions, empty boats, and discarded supplies). In total, the Japanese had lost more than 25,000 men, compared with a loss of 1,600 by the Americans. Each side lost 24 warships.

The first Medal of Honor given to a Marine was awarded to Sgt. John Basilone for his fighting during Operation Watchtower. According to the recommendation for his medal, he "contributed materially to the defeat and virtually the annihilation of a Japanese regiment."