His brother, Henry V, led a campaign against France in 1415. He was able to capture the city of Harfleur and went on to secure one of the greatest English victories of the Hundred Years' War, at the Battle of Agincourt in October of 1415. In 1416, Henry placed John in command of a fleet taking supplies to Harfleur, which overcame a fleet of the Franco-Genoese navy. Henry was able to capture the cities of Rouen and Caen and soon most of France was under English control.