@Gallo:
since you seem to know about this stuff :-D … can you please tell me what are the main characteristics a WW2 fighting-ship had to have in order to fell in each category? (roughtly speaking… destroyers; light, heavy and battle-cruisers, battleship, and so? (I think I can figure out why aicraft carriers and submarines are called that way :wink: ) thanks everybody about the feedback! :-D
WWII-era battleships were basically warships whose main armament consisted of heavy guns (meaning upward of 12" caliber, but in WWII terms typically in the 14" to 16" range, with some as big as 18") and whose armour protection was proportional to the main guns they carried (a rule of thumb being that the main belt armour was roughly as thick as the main gun caliber was large, in terms of inches or millimeters).
Battlecruisers were warships which, like battleships, carried heavy guns as their main armament (though typically fewer in number than a battleship), but whose armour was not proportional to their armament. Battlecruisers were much more lightly armoured. The theory was that they traded this lighter armour for greater speed. The battlecruiser concept suffered from two defects: in WWI, it already became clear that they were too vulnerable when fighting fully-fledged battleships (see the Battle of Jutland for details), and in WWII it became possible to have truly fast battleships which did not have to sacrifice armour protection to achieve high speed.
WWII cruisers, as I mentioned before, typically were either 8-inch heavy cruisers or 6-inch light cruisers. There were some oddities at both ends of the scale. The Deutschland-class Panzerschiffe (inaccurately dubbed pocket batttleships by the British press) can be regarded as ultra-heavy cruisers: over-gunned (6 x 11" guns), but under-armoured (I think their armour was considered marginal even by the standards of a normal heavy cruiser). At the opposite extreme, the British and the Americans (and I think the Italians) built some ultra-light cruisers armed with guns in the 5" range – notably for use as anti-aircraft platforms, like the British Dido class. Most cruisers carried some form of armour, though in some cases only a nominal amount.
Fully-fledged destroyers in WWII were ships typically combining a modest size, very high speed (around 35 knots), no armour (hence their nickname “tin cans”), modest guns (5" or so), but lots of torpedoes and anti-submarine weapons (depth charges of various types). Some destroyers were exceptionally large – so-called fleet destroyers, or destroyer leaders – and could almost count as small cruisers (see the British WWII Tribal class).
Destroyer escorts and frigates were basically economy versions of destroyers: similarly armed, but smaller and with less powerful engines delivering about 25 knots or so. They were meant to be inexpensive escort / antisubmarine vessels for convoy and battlefleet protection. They were developed as improved versions of the original “cheap and nasty” pure-escort vessels, the much smaller corvettes, which were even slower and had only one propeller. (Frigates, when they first appeared, were sometimes called “twin-screw corvettes”, which tells you something about what their perceived role was.)
These categories, over time, sometimes got blurred because of what is known as “weight/class inflation.” A vessel the size of a current-day frigate, for example, would have been considered a destroyer back in WWII.