On this day in 1776 the British Army, holed up in Boston, awoke to find that overnight Washington had extensive fortifications and 54 cannons on Dorchester Heights (a hill very close to Boston from which the Continental Army could bombard both the town and harbor.) At first the British planned to retake the hill by sheer volume of numbers with large losses expected, but after a heavy blizzard that night they wimped out and began the evacuation, by sea, of Boston. How did Washington do it? Pre-fab fortifications. The defenses were built out of sight of Boston and rolled into place over night. The idea was conceived by Lieutenant Colonel Rufus Putnam. Pretty cool, huh?