Battleships signified capital ships. In the pre-dreadnought era, battleships were rather small (7,500 tons to 10,000) tons with a mixed armament of large calibre guns (it varied according to the era) from 10" to 12" guns. Some earlier ships had 18" guns but these were muzzle loaders that required their guns to b e depressed for loading the powder and the the shell. In addition to the main armament, there was a secondary armament which varied in numbers. These could be 8" down to 6" or so, depending on the nation and the era. Finally, there were tertiary guns (like 6 pdr QFR) for defense against smallere vessels. There had been papers from the Italians who proposed an all big gun battleships. This theory was verified by the Japanese experience in the Russo-Japanese war of 1905. It was hard to distinguish betweene the shell splashes of teh medium and heavier guns. At about that time, the British adopted an all big gun, turbine geared ship that was both better armed, armored and faster than the pre-dreadnoughts (generally 18kts). The HMS Dreadnought had 10 12" guns in five turrets, could do an amazing 21 kts and rendered all previous battleships oboslete. The Americans actually launched the first ships (South Carolina class) with 8 12" guns in the A-B-C-D configuration but were slower to complete them. Additionally they were only 18kts. Soon all major naval powers followed suit and buit all big gun ships. However, while the secondary armament was deleted, the smaller lighter caliber guns (6" or smaller) were retained for defense against smaller craft (needed because they were faster and a higher rate of fire was required for defense). Most of these ships had 12'" guns with the Germans having the superior 11" (more accurate) guns. Eventually as WW I progressed the desire for firepower spurned the development of larger guns and 14"guns were adopted by the Royal Naval which later superceded it with the 15" guns found on the Queen Elisabeth and Royal Sovreign class battleships. Similarly the German Imperial Navy adopted the 15" guns in the Baden class battleships. These later bigger guns ships were called super dreadnoughts. In America the 12" gun of the South Carolina and later Arkansas classes were replaced with the 14" guns first introduced on the New Yoirk and Texas. !4" guns remained the mainstay of the USN until the 16" was adopted with the last three battleships constructed (West Virginia, Colorado, Maryland). WW I Admiral Jackie Fisher conceived of a fast cruiser armed with battleship caliber guns. He thought these would make excellent raiders in the Baltic Seae and thus the battlecruiser was born. Faster than a battleship (26 - 30 kts), they were armed with 12" guns like a battleship. The tradeoff was they were lightly armored. The Germans built their own too but armored them very well (as seen at the Battle of Skagerrat/Jutland) where British battlecruisers blew up and German battlecruisers took a lot of punishment (with most still getting home). Cruisers were smaller ships design for scouting for the battlefleet and for trade protection. They were faster, carried lighter armor and had longer range than the battleships. The size of the cruiser varied on time and navy. Early cruisers were small affairs which were about 2k tons and armed with 4.1 in (105 mm) guns). Larger cruisres had 5-6" guns. Standards change and by WW 2, it was decided to classify cruisers by their gun calibers and not their size. Cruisers armed with 6" guns were light cruisers and those with 8" were heavy cruisers. Before the dreadnought the "armored" or "protect cruisers" were built by most navies. They had medium caliber guns (8-9.2" guns), could do about 18-21 knots and some protection. However, the advent of the battlecruisers made that entire genre of ship obosolte. Still they saw some serivce in WW I. Cruisers in WW II became more specialized. For example, both the USN, IJN and RN had cruisers built or converted into AA defense ships. For a while the IJN also had torpedo cruisers (most of the armament was torpedo tubes). The Germans in the antebellum years were under the restrictions of the Versailles Treaty. They could only replace their pre-dreadnought ships with a ship under 10k tons and armament no bigger than 11". It was figured that the Germans would use that tonnage to build either a 8" cruiser or a coastal defense battleship (slow, 12" guns or so). The Germans did neither. Instead they designed a cruiser sized ship armed with WW I caliber 11" guns (of course, new 11" guns which were longer ranged than the WW I counterparts). Dubbed by the British pocket battleships, they were known to the Germans as Panzerschiffs (armored ships) better armed than any cruisere and faster than most battleships. Hencee their motto, Faster than Stronger, Stornger than Faster. The only ships they need fear were the British battlecruiers (and the French ones). When WW II broke out the Kriegsmarine reclassed them as heavy cruisers. The Graf Spee was the most famous of the trio (Admiral Scheeer and Lutzow/formerly Deustchland). Destroyers were small ships that often served as scouts or screeners for the fleet. They were dubbed destroyers because their mission was to destroy the fear torpedo boat. I'm not talking about McHale's Navy size PT boats but small, bast ships armed with torpeodo tubes (some of them were a little larger than the WW I destroyer). Torpedo boats were thought to be able to evade the defensive fire of the battleship and with a cheap well placed torpedo could sink a battleship. To protect the battleships destoyers were created. They were larger, carried torpedoes and more guns than a torpedo boat. Starting in WW I destroyers were just a bit larger than a torpedo boat but by WW 2 some destroyers weere larger than early WW I cruiser! In the day of sail, frigates were supposed to be escort ships and scout ships. In the modern era they were escort ships armed with smaller guns than a destroyer and meant to protect convoys from wolf-packs. Corvettes were even smaller and could be built cheaply but were very useful for convoy escort work. Neither of these ships were armed with torpedo tubes.