From Leading Events of Maryland History:
In August, 1814, another British fleet arrived in the Chesapeake, commanded by Admiral Cockrane. On board this fleet were three thousand veteran soldiers under General Ross. An expedition for the capture of Washington was planned at once. Sir Peter Parker was sent up the bay with several vessels to threaten Baltimore and annoy the people as much as possible.
A map of the U.S. Troops' attempt to protect Washington.