The cruiser is, per definition, the smallest ocean-going warship capable of independent operations, meaning operations in which the cruiser is the largest capital ship. This definition, though not made by me, is one I thoroughly agree with.The design of a cruiser is as old as the maritime history itself; but in earlier times, as in the Napoleonic area, virtually all ships that could sail the oceans in navies were cruisers. Their endurance, only limited by the amount of fresh water and food they could take, allowed sloops, frigates, and men-of-war to cruise the seven seas for quite a long time. 

     This paragraph adds in another important feature of most cruisers, that of their high endurance.   
     The problem to build a real cruiser first came up with the ability to make ships from whole steel and steam engines, the latter seriously reducing any such driven ships' endurance.   
Along with the design of new battleships, or ships-of-the-line, thus came the construction of two types of cruisers: armoured cruisers, which were intended to serve in "real" fleet actions, meaning battles, and light cruisers, that, with their lighter armament and armor could carry more coal and thus go further.   

     It was Admiral Lord Fisher of Dreadnought fame that ended the career of the armoured cruiser with his battlecruisers. Sharing an equal armor basis, the battlecruisers were faster and better armed than any contemporary armoured cruiser. 

    Having no real mission in the naval world anymore, the armoured cruiser, slow, and vulnerable, was soon discarded by most fleets.   
    However, oil propulsion, and turbines, promised a way to get a cruiser with larger guns than a light cruiser to light cruiser speeds. The British Hawkins class of 1919 was the first step into that direction, having seven 190mm guns and the speed of a light cruiser.   
Just as these cruiser started becoming a trend, however, the Washington Naval Treaty cut seriously into any navy's conceptions. Made up by politicans hoping to restrict the world from senseless build-up of naval forces, it stated that:   

1. 10.000 tons was to be the maximum displacement of ANY cruiser, Light or Heavy
2. 203mm was to be the maximum caliber for Heavy Cruisers
3. 155mm was to be the maximum caliber for Light Cruisers

    The United States had, as its only modern cruiser class, the light cruisers of the Omaha class. These were still highly influenced by the old style of casemates. They carried four guns 155mm in two twin turrets, one each for and aft, and added to that six 155mm in casemates, four firing forward, two aft. Build to operate as the "eyes" of th fleet, they were fast, and had two catapults for seaplanes. 

    There was a long period of nothing after these ships were build.   
The first of the "Treaty-Cruisers" appeared in 1930. USS Pensacola and sister Salt Lake City were the most powerful cruisers of their time. They carried with them ten 203mm guns in two triple and two twin turrets, placed in a superfiring fore-and-aft scheme, which was unique as the heavier triple mounts were superfiring. 

    Though they carried torpedos when commisioned, these were removed before the war.   
Following this class of ships was the Northampton class, setting the trend for all following Heavy Cruisers. Deleting one 203mm gun, they held nine 203mm guns in three triple turrets, one aft and two superfiring forward. These ships also carried torpedos until 1935, as did the Pensacolas, when they were removed and the 127mm armament was doubled from four to eight. 
  
    The successor of this class was the Portland class, of two ships, which was commisioned in 1933. It was three meters longer and had slightly heavier armor, finally using the 10000 tons limit fully. The same armament characteristics applied. 

    Both Portlands were fitted as flagships, and Indianapolis frequently carried VIPs.   
These flagship fittings were extremely important later, as the follow-on class, the New Orleans retained no single ton of space to fit flagstaff compartments. These ships were quite useful, using, again, every ton.   

    As the first class of Light Cruisers build in the United States with turret-only main armament, the Brooklyn class had a rather unusual appearance for a US cruiser. Probably triggered by both the Japanese Mogami, from which the main armament was gleaned, and the Takao class, which helped with the turret arrangement, these ships carried fifteen 155mm in five triple turrets, two each superfiring fore and aft and a third forward, between the bridge and the superfiring gun turret, facing aft.   

    Two of these St. Louis and Helena carried their secondary armament, eight 127mm guns in four enclosed twin turrets, two on each side. The other ships carried them in open mounts until a late-war refit.   

    USS Wichita the last Treaty Heavy Cruiser build in the United States looked very similiar to the Brooklyns but carried 203mm guns in the usual arrangement, though her turrets were of a later and better design than those mounted in the earlier ships.   

    Wichita was kind of a connection between Treaty Cruisers and non-Treaty Cruisers.   
When in 1936 the London Naval Treaty was concluded, further limitations were laid upon cruiser construction. As heavy (in terms of tonnage, now) cruisers were not allowed to be build (Ed: What were the limits for Heavy and Light Cruisers respectively?), the United States, which saw itself confronted with Japanese destroyers that had larger armament than U.S. destroyers, and the ever increasing danger from planes, decided to build a cruiser-sized ship with dual-purpose weapons.   

    The Atlanta class carried a powerful AA armament, eight twin 127mm turrets, which were placed in a rather curious fashion, three turrets superfiring fore and aft, plus one each at the ship's sides, firing aft.   

    These vessels were excellent AA ships, though their usefullness was somehow limited because for it's sixteen guns, it had only two directors.   

     This class was successful enough to be build again between 1942 and 1946, making up the Oakland class. These vessels were basically Atlantas without the two turrets on the flanks.   

    The war in Europe had already waged for a year when in 1940 the first class of non treaty-restricted cruisers was laid down. The Cleveland class sacrificed the Brooklyn's C turret, which had a rather limited field of fire anyway, for better protection, range and AA firepower. The reduced weight from the removed turret was thus filled with six 127mm twin turrets for AA protection, the same which gave the Atlanta's their firepower. The main armament consisted of twelve 155mm guns in four triple turrets, two each superfiring fore and aft. They were not superships, but their good design and the need to have many ships of a somewhat standard design resulted in the construction of 27 of these cruisers, of 39 originally conceived.   

     To these, one could count the concepted 13 Fargo class ships, not detailed here. They had only one smokestack, but were otherwise the same ships as the Clevelands. Only two were, build and they were only commisioned after the war.   

     Of the ships that were able to serve in the Pacific War, the next class was the Baltimore class of heavy cruisers, based on the Cleveland design, but eliminating through more proper design the Clevelands disturbing top-heaviness. Their 203mm guns were in the same turret design as those of Wichita. These fine heavy cruisers were a valuable addition to the US Navy's carrier escorts, and some were later given guided missile armament.   

    The last class of ships I will show here will probably arise some argument. I decided to put the Alaska class here, instead of in the battleships section. Concepted to act as anti-merchant-raider vessels, they featured nine 306mm guns, made especially for them, and mounted in three triple turrets in the usual arrangement. As the Japanese merchant raiders, which to counter they were build, were never build, four of the six scheduled ships of the class were cancelled. The other two, Alaska and Guam, were used as carrier escorts, but served only three years.   

    U.S. cruisers were not only the prime carrier escorts, but also the largest surface warships that fought frequently in surface engagements. The pre-war Heavy Cruisers formed the core of the U.S. forces that fought in the Guadalcanal campaign, and they took heavy losses during the war.   

    It was soon found out however that Light Cruisers were the more effective means of destroying destroyers, and thus, U.S. forces relied on them for surface battles. They, as well, took serious losses. 
To a large part, these losses were unnecessary, sometimes dumb; but they helped create ideas and tactics to defeat the Japanese - and they helped win the war.   

    After this, I want to clarify my opinion on one point, that of the lacking torpedo armament on US cruisers. Those who have stated that the US cruisers were at a disadvantage without them, and that their removement was a great failure, seem not to understand the situation that the US was to find in battle. The first problem is self-inflicted: US cruisers, relying on their line-of-battle combat tactic, were trained to fight the battle from long-distance. Besides the First Battle of Guadalcanal, there was no situation in which the short-ranged US torpedoes could possibly have inflicted hits.   

    Second, it is a proven fact that, during the four surface engagements fought in 1942, in all of which US torpedoes were present, at best ONE hit, one of USS Farenholt or Duncan on Furutaka during the Battle of Cape Esperance (this hit could as well have been shell fire). As well, the best realistic estimate of US torpedoes hitting a stationary, clearly visible target at the time was three in eight (given by Frank, Guadalcanal, in the chapter on Santa Cruz).   
In NONE of the battles in which cruisers were present, sparing Empress Augusta Bay, was a torpedo attack part of the employed tactics. In Empress Augusta Bay, the US cruisers were too far away from the enemy formation; a torpedo attack would have been useless.   
It remains the fact that the DESTROYER was the ship of choice for the torpedo; while the employment of torpedoes in Japanese cruisers was okay in the early Guadalcanal battles, the later Empress Augusta Bay, fought at about the time when US tactics as a whole were starting to take effect, rendered the Japanese cruiser's torpedoes useless.   
To state, that the removement was foolish (my wording), is under these conditions dumb, because it fails to see that it was not the torpedo tubes, or lack thereof, that was the US disadvantage, or would-be advantage, but the faulty torpedoes and tactics. Phew, sorry for staying on the soapbox so long...back to the US cruisers.

Pre-Treaty Cruisers
CL-4 Omaha class 

Treaty Cruisers
CA-24 Pensacola 
CA-26 Northampton 
CA-33 Indianapolis class 
CA-32 New Orleans class 
CL-40 Brooklyn class 
CA-45 Wichita class 
CL-51 Atlanta class 

Wartime Cruisers
CL-55 Cleveland class 
CA-68 Baltimore class 
CB-1 Alaska class