The Japanese battleship Yamato and her sister ship, the Musashi, were the largest battleships ever built. She displaced 72.8 tons at full load and bore the largest naval guns ever mounted to a ship at 18.1 inches (previous record was 18 inch guns. Shows the spirit of one-ups-man-ship some military designers have.) Due to the vast amount of resources that go into maintaining a battleship and the relative firepower advantage of aircrafter carriers demonstrated in WW2, most countries have ceased production of these mammoth warships.
By the end of WW2 both were destroyed, and likely ships of their kind won't be built again anytime soon. Until cannon technology (ie railgun tech) improves significantly, the value of these titans is minimal.