<P> After withdrawing from Boston , Howe immediately began preparations to seize New York which was considered the ' hinge ' of the colonies . In late August , 22,000 men ( including 9,000 Hessians ) were rapidly landed on Long Island using flat bottomed boats , this would be the largest amphibious operation undertaken by the British army until the Normandy landings almost 200 years later . In the ensuing Battle of Long Island on August 27 , 1776 , the British outflanked the American positions , driving the Americans back to the Brooklyn Heights fortifications . General Howe not wishing to risk the lives of his men in a bloody frontal assault then began to lay siege works . The navy had failed to properly blockade the East river which left an escape route open for Washington 's army , which he fully exploited , managing a nighttime retreat through his unguarded rear to Manhattan Island . British forces then fought a series of actions to consolidate control of Manhattan Island , culminating in the Battle of Fort Washington which resulted in the capture of close to 3,000 Continental troops . Following the conquest of Manhattan , Howe ordered Charles Cornwallis to `` clear the rebel troops from New Jersey without a major engagement , and to do it quickly before the weather changed . '' Cornwallis ' force drove Washington 's army entirely from New Jersey and across the Delaware River . However , in the pre-dawn hours of December 26 , Washington crossed back into New Jersey and captured a garrison of Hessians at Trenton . Several days later , Washington outmaneuvered Cornwallis at Assunpink Creek and overwhelmed a British outpost at Princeton on January 3 , 1777 . Cornwallis rallied and again drove Washington away , however the defeats showed the British army had become too overstretched and Howe abandoned most of his outposts in New Jersey . </P>
where did the british army launch a successful invasion in 1776
Long Island