On this date in 1918, the Germany attacked America!
Well, the Kriegsmarine attacked Massachusetts.
Actually, one U-Boat shelled and sunk a tug off the town of Orleans on Cape Cod, and took a few potshots at the surrounding environs for good measure. Some U.S. Navy seaplanes showed up, some bombs were dropped, the sub gave it up for a bad idea and slunk off to do more normal U-Boaty-type things such as torpedo merchantmen, and everybody involved professionally in the matter seemed a little embarrassed about the whole incident.
Of course for quite some time afterward, every trick of light, loud noise, or low-flying seagull along the east coast was reported as a Jerry submarine.
Incidentally, the U-Boat attack on Orleans was the first time American soil had been fired upon by foreign troops since the War of 1812.