April 15, 1917 is the first date for which a serviceman can be awarded the Purple Heart for "Being wounded or killed in any action against an enemy of the United States or as a result of an act of any such enemy or opposing armed forces".
An earlier award of a similar name, and which inspired this medal, was designed and authorized by Washington during the Revolution as the Badge of Military Merit. It passed into disuse following the Revolution. Following World War One, however, the medal was revived in 1932, after several years of consideration, and awardable to men who had received the Meritorious Service Citation Certificate, Army Wound Ribbon, or were authorized to wear Wound Chevrons subsequent to April 5, 1917, thereby catching every serviceman who qualified who had served in World War One but sadly omitting men who had been wounded during the Punitive Expedition that had immediately proceeded it. 320,518 medals were awarded for service during World War One.
Douglas MacArthur was the first U.S. serviceman to receive the modern award.