In the interwar years, there was a great deal of attempt made to put naval arms limitations in place, which ultimately were failures. For one thing, Germany wasn't included since it was limited by the Versailles treaty, and for another different nations had different needs. For example, the limit for cruisers was 10,000 tons, but there was much wrangling over whether fuel and other load was part of the limit. For Britain, with far-flung posessions, and needing more fuel for its ships, that would penalize them in combat power against their opponents, and the same was to a degree true for U.S. ships, while Italian and Japanese ships would have an advantage. In any case, Japan and Germany eventually just violated and then repudiated their treaties.
However, the Battlecruiser, because of the tonnage limitations of these treaties became unpopular. The U.S. finished none (officially) it's WWI battlecruiser became aircraft carriers or were scrapped unfinished. Britain reduced its fleet to only 3 (
Repulse, Renown, and Hood) and Japan reconstruced its
Kongo-class battlecruisers as battleships. In some sources they are still called battlecruisers, however.
This is where the blurring of designations starts to appear: A destroyer or a purpose-built battleship is easy to identify. But what is a cruiser? A light cruiser, with typically guns about 155mm (6 inches) is, in many respects an enlarged destroyer. It has a different purpose however; a destroyer will have more antisubmarine equipment in this era while a cruiser while focus more on surface targets. Displacement, however, tells us nothing since a light cruiser in WWII such as the
Cleveland-class might displace over 11000 tons, almost as much as a pre-dreadnought battleship!
Gun size is a better rule; typically light cruisers had 155mm or smaller guns and heavy cruisers larger; 8-inch being most common (this was an argument against heavy cruisers since very few ships could resist 6 inch but not 8-inch hits.
However, there are a few ships that confuse the issue. In addition to the redesigned
Kongos, there are the German
Sharnhorst-class ships and the
Deutschlands, and the U.S.
Alaska-class.
The
Scharnhorsts had 9x 11-inch guns, comparable to WWI German battlecruisers, but battleship-like armor. In fact, they were designed for 6x15-inch guns but since the turrets were not available yet they were mounted with the 11-inch in the interim. 6x 15 would have been the same armament as
Repulse and
Renown. By WWII standards they were very small battleships, but much too large and heavily armed to be cruisers. British sources therefore refer to them as Battlecruisers, while German sources refer to them as battleships, and a convincing argument can be made either way; this highlights the blurry line between types. My personal choice is battlescruier, based on the fact that Scharnhorst was no match for
Duke of York and was sent to the bottom relatively easily by the British ship.
The
Desutschland-class; the most famous being
Admiral Graf Spee and
Admiral Scheer were referred to by the Germans as
Panzerschiffe or armored ships, and actually complied with the Versailles treaty with a little creative math. They had 6x 11 inch guns in two triple turrets rather than three twin. They were the only class I know of that could resist 6-inch but not 8-inch fire, and they were used as commerce raiders.
For all intents and purposes they were heavy cruisers with a very large but impractical main battery, and heavy armor. In practice, the design was really not very good because one turret being disabled meant a 50% loss of firepower (and ALL firepower to either fore or aft) and because you really do not need 11-inch guns to sink merchant ships. The reason these ships are blurry is the 11-inch guns which confuse people who think "all heavy cruisers must necessarily have 8-inch" (which is a rule of thumb) and because they have received the appellation "pocket battleship", which is more an appelation to what can be crammed into a ship of that size; they are not battleships in any sense. It further has occasionally caused the
Scharnhorsts and
Bismarks to be cvalled pocket battleships, which is also not accurate unless possibly comparing
Scharnhorst to
Yamato.
The
Alaska-class, with 9x 12-inch guns, high speed, and reasonable armor, blurs the designation ebcause of the political baggage of the word "battlecruiser". Officially, they were designated "large cruisers" and given hull numbers with the CB designation rather than the CC that the uncompleted WWI-era battlecruisers were given. In reality, however, they are battlecruisers in every sense of the word. The designation "large cruiser" really performs no useful function or highlights any meaningful difference from a battlecruiser. Some people have gone so far in defending this differentiation as to highlight the placement of
Alaska's 5-inch secondary armament; a rather silly argument since placement of secondary argument is a nitpick in broad typing of warships. "Large Cruiser" is really an unnecessary designation that serves no purpose (unless you're Russian, in which case you use a different typing system anyhow).
These links contain an excellent comparison of the various post-treaty battleships of WWII
http://www.chuckhawks.com/post_treaty_battleships.htmhttp://www.chuckhawks.com/post_treaty_battleships2.htmtreaty battleships
http://www.chuckhawks.com/treaty_battleships.htmbattlecruisers and the aforementined line-blurrers
http://www.chuckhawks.com/battlecruisers.htmheavy cruisers; parts 2 and 3 can be acccessed at the bottom of the page
http://www.chuckhawks.com/heavy_cruisers.htmGenerally, however, WWII makes it easy: A destroyer is a small ship with 5-inch or smaller guns that protects from subs and aricraft primarily, A cruiser is s middle-sized warship with 6-to-11 inch guns that provides fire support and antisurface warfare as well as antiaircraft protection, a battlecruiers is larger than a cruiser, with guns of at least 11 inches but which cannot stand up to a battleship, and a battleship is a large warship with guns bigger than 12 inches and which can be expected to fight any other ship in direct fire with at least some chance of survical depending on the circumstances.
Moving on to the postwar era up to the 80s in the next post.