On June 14, 1775, the Continental Congress voted to replace the part-time militias that were facing off against British forces with a full-time army. After 1,300 battles and skirmishes, the Army, led by Gen. George Washington, defeated the British Empire, winning our independence. CBS News national security correspondent David Martin looks at the creation of America's unified military, and visits a National Museum of the United States Army exhibit honoring the sacrifices of our nation's revolutionary heroes.