The Union Navy in 1861 was relatively small but, by 1865, expanded rapidly to 6,000 officers, 45,000 sailors, and 671 vessels totaling 510,396 tons. Its mission was to blockade Confederate ports, control the river system, defend against Confederate raiders on the high seas, and be ready for a possible war with the British Royal Navy. The main riverine war was fought in the West, where major rivers gave access to the Confederate heartland. The US Navy eventually controlled the Red, Tennessee, Cumberland, Mississippi, and Ohio rivers. In the East, the Navy shelled Confederate forts and supported coastal army operations.