Heavy cruisers were the only type of cruiser defined specifically by the 1922 Washington Naval Conference. Such ships, obsolete for modern uses, had main batteries between 6.1 and 8" naval gun/203mm, some armor, and, for treaty compliance, a displacement not to exceed 10,000 tons.
Heavy cruisers were flexible and useful ships. Before the extensive use of aircraft and submarines, they balanced speed, protection, and armament well enough to be able to conduct independent missions, especially for commerce raiding. They were scouts for battleships. In amphibious warfare, they were excellent gunfire support ships, using both their main and secondary batteries. Japanese heavy cruisers had significant torpedo armament. Heavy cruisers and battleships could thicken the antiaircraft defenses around aircraft carriers, yet be survivable.
After the Second World War, heavy cruisers were large enough to be converted to incorporate new guided missile technologies. The U.S. even built one postwar gun-only heavy cruiser class, which proved useful as a flagship and for naval gunfire support.
Armored gun cruisers, however, no longer have a role in a world of highly lethal guided missiles. While the U.S. Ticonderoga-class carries out many of the same functions, that class is first and foremost an area air defense platform, with secondary roles in anti-surface warfare, anti-submarine warfare, flagship and naval gunfire support. Zumwalt-class destroyers, with 155mm guns, may be the closest type to a treaty heavy cruiser.