His plan was to blockade the Confederacy's coastline and control the Mississippi River valley with gunboats. Lincoln ordered a blockade of the southern seaboard from the South Carolina line to the Rio Grande on April 19 and on April 27 extended it to include the North Carolina and Virginia coasts. On April 20, the Union Navy burned and evacuated the Norfolk Navy Yard, destroying nine ships in the process, leaving only Fort Monroe at Old Point Comfort as the last bastion of the United States in Tidewater Virginia.