 Merchant Ships and American Entry into World War I", historian Dr. Rodney Carlisle asserts that it was, in fact, the sinking of nine U.S. merchant ships that utilmately induced President Wilson to ask Congress to declare war.Over time, the use of defended convoys of merchant ships allowed the Allies to maintain shipping across the Atlantic, in spite of heavy loss.The Royal Navy had conducted convoys in the Napoleonic Wars and they had been used effectively to protect troopships in the current war, but the idea of using them to protect merchant shipping had been debated for several years.