The War at Sea between 1914 and 1918 was mainly between two great fleets, Britain's Royal Navy and Germany's Imperial Navy. The Sea War encompassed all the world's oceans. It also saw the development of new naval weapons and battle tactics. The German and British Navy's each had 2 roles. One was to destroy the others battle fleet and the second was to destroy the enemy's merchant shipping. Both sides went to war in 1914 with both these roles given priority. In modern times, the Navy tend to concentrate their fleets around the giant aircraft carriers. In 1914 however and later in 1939, it was the battleships that were the fleets flagships. These were the largest types of warships afloat and they had the biggest guns.