In the summer of 1777, Vice-Adm. Richard Howe arrived in Chesapeake Bay with 15,000 soldiers. Meanwhile, Washington had been reorganizing the Continental Army, made possible in part by secret French aid. The opposing forces met at Brandywine Creek, southwest of Philadelphia, on September 11, 1777. Outnumbered American soldiers were surprised by British tactics and forced to retreat toward Chester. Major General Nathanael Greene led the retreat, successfully preserved his soldiers and delayed the British occupation of Philadelphia. The British seized the city on September 26, sending the Continental Congress scurrying. On October 4, Washington conducted a surprise attack on British forces encamped at Germantown, north of Philadelphia. In the early stages of the assault it appeared that the Americans would prevail, but battlefield confusion led to retreat. This was attributable to losses from "friendly fire" and fatigue induced by a 35-mile march prior to fighting the four-hour battle. The Continental Army then retired to Valley Forge for the winter.