September 1915—as the American watched, the German pilot rose up in the rear cockpit of his biplane and saluted smartly. A split second later, an explosion ripped through the fuselage of the enemy plane, blowing it into two pieces and sending it hurtling to earth.

This bizarre accident began as Sgt. Bert Hall of Kentucky was flying inside German lines between Rheims and Machault at 14,000 feet. He was surprised as the German flew above him and tossed the first of several aerial hand grenades. Hall was close enough to see him pull the fuse pin of his last Fliegermaus—and to observe the enemy's wild scramble as he dropped the grenade in his own cockpit. Six seconds later the episode ended.

Bert Hall was an almost legendary soldier of fortune. In 1909 he went to France, where he learned how to fly from Bleriot and the Farmans. Before the war, he was the sole member of the Bulgarian air force, then switched allegiance and served the Sultan of Turkey. Hall was living it up in Paris following a barnstorming tour of Europe when World War I was declared. The next day he joined the French Foreign Legion, the only French armed service that would accept non-citizens.

Hall was a founder of the Lafayette Escadrille, a French squadron made up of American volunteers. In 1917 he barely escaped from Russia with his life. In the late ‘20s he became known as Gen. Chang Hui-Chang, serving both the Nanking and Canton governments. Adventurous Bert Hall died at home in a Midwest auto accident in 1948.