April 12th had a few interesting things happen:

1862 - Confederate forces fired on Fort Sumter, leading to the Civil War.  Interestingly, the only deaths occurred after the battle when departing Union forces fired a salute and two soldiers were killed by premature cartridge explosions.

1861 - John Andrews led Union volunteers in capturing a Confederate train near Marietta, GA, and headed north destroying rail and telegraph lines as they went. Pursued by Confederate forces, those that didn't escape capture were killed by the Confederates. Some of the raiders became the first to be awarded the Medal of Honor.

1944 - FDR dies in Hot Springs, GA, resulting in Harry Truman becoming President.

1979 – LT(jg) Beverly Kelley assumes command of the USCGC Cape Newagen, becoming the first woman to command a U.S. warship.

1994 - Husband and wife immigration lawyers Canter and Siegel unleashed the first commercial spam to USENET, the Green Card spam, by posting about their services across thousands of USENT groups. USENET struck back by finding and posting personal and professional information about C&S, and Joel Furr creating one of the first commercial USENET tchotchkes, The Green Card Spam T-Shirt. (Yes, not military history but I remember the spam well)

2009 - US naval forces rescue Capt Richard Phillips of the MV Maersk Alabama, with SEALs killing 3 of the pirates involved in the abduction.