From the National Park Service:
On December 25, 1776, General George Washington and a small army of 2400 men crossed the Delaware River at McConkey's Ferry, in Bucks County, Pennsylvania, on their way to successfully attack a Hessian garrison of 1500 at Trenton, New Jersey. This march, at one of the lowest points of the American Revolution, gave the Patriots new hope after their failed effort to keep the British from occupying New York City. The close of 1776 found the cause of American independence from Great Britain staggering under a succession of defeats. In October, the Continental Congress had made provision for a long-term military force, but at the end of the year this establishment was on paper, not in the field where it was desperately needed. Washington, in his camp on the Pennsylvania side of the Delaware, realized that he must strike a military blow to the enemy before his army melted away and he was determined to hit the Hessian garrison at Trenton. On the night of December 25, the American main force was ferried across the Delaware River by Colonel John Glover's Marblehead fishermen and in the bleak early morning hours assembled on the New Jersey shore for the march on Trenton, about 10 miles downstream. Surprise was complete, and within an hour and a half after the action opened the Hessians surrendered.
