The Confederacy relied on external sources for war materials. The first came from trade with the enemy. "Vast amounts of war supplies" came through Kentucky, and thereafter, western armies were "to a very considerable extent" provisioned with illicit trade via Federal agents and northern private traders. But that trade was interrupted in the first year of war by Admiral Porter's river gunboats as they gained dominance along navigable rivers north–south and east–west. Overseas blockade running then came to be of "outstanding importance". On April 17, President Davis called on privateer raiders, the "militia of the sea", to make war on U.S. seaborne commerce. Despite noteworthy effort, over the course of the war the Confederacy was found unable to match the Union in ships and seamanship, materials and marine construction.