Hemmed into a small enclave around the town of Brooklyn, General Washington and about 9,000 of his troops faced an uncertain fate as Clinton and around 15,000 redcoats began bringing forward hundreds of cannon to batter the patriot army. Taking advantage of favorable winds and dense fog which blanketed the region on 30 August, Washington moved his troops across the East River and into New York City without alerting the British until they were gone. A royal naval officer, Capt. Sir George Collier, recorded his dismay at Washington’s escape and predicted that the war might continue far longer than British authorities had first expected.
"To my inexpressible astonishment & concern the Rebel army have all escaped across the River to New York! how this has happened is surprising... now I foresee they will give us Trouble enough, and protract the War, Heaven knows how long."
Captain Sir George Collier, Commander of the HMS Rainbow/The war in America by Admiral Sir George Collier, 1776.