Watch WWI: The First Modern War Season 1 Episode 4 Online

The Atlantic became a killing field as German submarines took on the might of the dominant British Navy. The stealth and silent killers were able to sink 5,200 ships by war's end, and nearly brought Britain to its knees. But in their frenzy of attacks, the Germans sink the US passenger liner Lusitania, killing nearly 2,000 on board. American outrage helped President Wilson get Congress to finally agree to enter the war. In the end, the Allied Atlantic blockade forces Germany to surrender, but the submarine was established as an effective military weapon.