The campaign to seize Philadelphia, the second mayor phase of British strategy in 1777, began in late July. Some 15,000 troops under Howe's command sailed from New York on 23 July and landed at Head of Elk (now Elkton), Maryland, a month later (25 August). Washington, with about 11,000 men, took up a defensive position blocking the way to Philadelphia at Chad's Ford on the eastern side of Brandywine Creek in Pennsylvania. Howe attacked on 11 September, sending Cornwallis across the creek in a wide-sweeping flanking movement around the American right, while his Hessian troops demonstrated opposite Chad's Ford. Maj. Gen. Nathanael Greene's troops staved off Cornwallis' threatened envelopment of Washington's whole force, and the Americans fell back to Chester in a hard-pressed but orderly retreat. Patriot losses in this engagement totaled about 1,000 killed, wounded, and prisoners. British casualties were less than 600.