The largest Navy in the world, by tons of ships, is the United States Navy at nearly 3.5 million tons. By tons the U.S. Navy is about as big as the other ten biggest navies in the world combined, and most of those nine are allies. Our nearly 3.5 million ton Navy is roughly four times the weight of our next nearest competitor, Russia, which comes in at about 850,000 tons. The advantage is particularly telling in aircraft carriers. With a dozen them the United States has the only truly operational super carriers in the world (the Chinese Varyag is not really ready yet for full carrier operations). The other carriers that other Navies have are smaller, and more akin to our also numerous helicopter/assault carriers.
The United States military budget is double Russia’s and China’s combined.