Watch World War 1 in Color online: Episode 4 Killers of the Sea

Naval rivalry between the empires of Britain and Germany had played a major factor in the build up to World War 1. When the conflict began, the opposing admirals expected that the naval war would be settled by a massive clash between the two fleets of battleships. But in reality, fear of losing their ships meant that both fleets stayed in port for the first two years, and when the great battle did come - at Jutland in 1916 - it was indecisive. Instead, the naval war became one of blockade and new technology. The British swiftly put a stranglehold on all German overseas trade, and gradually began to starve the country. The Germans responded by using a new and as yet untried weapon - the submarine.

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