June 21 in Military History

Wellington decisively defeats the French army of King Joseph Bonaparte in Spain, effectively ending French rule in the Iberian Peninsula and freeing Wellington to invade southern France.

Union forces under Grant launch the first major offensive to cut the Weldon Railroad south of Petersburg, testing Confederate defenses in the opening phase of the long siege.

The cruiser USS Charleston and a Marine detachment capture Guam from Spain without a fight, the Spanish garrison was unaware that war had been declared.

Empress Dowager Cixi formally declares war on Britain, France, Germany, Italy, Austria-Hungary, Russia, Japan, and the United States, triggering the Siege of the International Legations in Peking.

Rear Admiral Ludwig von Reuter orders the scuttling of the interned German High Seas Fleet at Scapa Flow, sinking 52 warships to prevent them from being distributed among the Allies.

Rommel's Afrika Korps captures the fortress of Tobruk in a single day, taking 33,000 Allied prisoners and vast quantities of supplies, one of the worst British defeats of the war.

Organized Japanese resistance on Okinawa ceases after 82 days of the bloodiest battle of the Pacific War. Over 12,000 Americans, 110,000 Japanese soldiers, and up to 150,000 Okinawan civilians died.

The U.S. Navy forms the Deep Submergence Systems Review Group following the loss of USS Thresher, launching a program that produced deep-rescue vehicles, SUBSAFE, and modern submarine safety standards.

Argentine forces in the Falkland Islands formally surrender to British Major General Jeremy Moore, ending the 74-day Falklands War.

Pilot Mike Melvill flies SpaceShipOne past the 100 km Karman line in a suborbital hop over the Mojave Desert, the first crewed spaceflight funded entirely by private capital.