The most controversial class was the battlecruiser, initially a fast, heavily armed but less well armored kind of battleship. British battlecruiser losses during the Battle of Jutland in 1916 cast doubt on the battlecruiser concept. And by the late 1930s, a new generation of battleships appeared that were fast as well as strongly armed and armored, thus eliminating the justification for the battlecruiser class.
Cruisers were not controversial, but problematical. And what was problematical was how to conceptualize suitable designs to fit a variety of potential roles within the constraint of naval construction budgets and constraints imposed during the inter-war period when naval limitation treaties were in effect. For example, cruisers were useful for "showing the flag" and maintaining a degree of peace and order in dangerous parts of the world; this was a major role for Royal Navy cruisers stationed far from the United Kingdom. Cruisers could be useful as commerce raiders, something that appealed to the German navy. Cruisers could be useful for sweeping commerce raiders from the sea. Cruisers were useful as long-range scouts for a battleship fleet. Cruisers were useful for screening battleship fleets and carrier task forces from attacks by enemy cruisers and torpedo-armed destroyers. They were useful for providing anti-aircraft protection for fleets and task forces.
The trouble was, one kind of cruiser did not equally satisfy all those tasks. Those naval treaties eventually codified two kinds of cruisers, light and heavy, the difference being in their armament. Light cruisers were limited to 6-inch (about 15 cm) guns that usually were fast-firing, smothering their target with shellfire. Heavy cruisers could have 8-inch (about 20 cm) guns that would be effective against similarly armed opponents, but had a comparatively slow rate of fire that made them less effective for close-range, rapidly moving combat. How many of each kind of cruiser should a navy build?
The American navy was at a disadvantage compared to other navies due to treaty weight restrictions. This was because US cruisers had to be able to operate at Pacific Ocean distances and potential opponents' cruisers could be shorter-range. Given the treaty limit of 10,000 tons displacement, American cruisers had to sacrifice some combination of armor, speed (related to power plant weight) or armament in order to make room (and weight) for attaining those long cruising ranges.
Until World War 2 when the aircraft carrier emerged as the most important kind of warship, battleships were the decisive element of naval power. Cruisers were always secondary, given their support roles noted above.
Yet to the general public, it could be hard to tell cruisers apart from battleships when casually viewing them. That was in part because they tended to look similar to each other and different from destroyers, aircraft carriers and such. Another factor is that cruisers tend to be long -- as long or longer than battleships, even. Although they were long, they were narrower than battleships because they had to have a high fineness ratio (length divided by width) to attain high speeds. And so they weighed considerably less than battleships of similar length, having less armor and smaller, lighter guns as well as the less width.
The photo above, taken in 1944, offers a comparison between America's largest class of battleship and its largest class of cruiser. The Alaska's overall length, 808 feet (246 m), is more than 9/10ths of the Missouri's 887 feet. And that 808 feet was greater than the length of the two other World War 2 classes of American battleships, the North Carolinas (729 feet) and the South Dakotas (680 feet) or of the last pre-treaty battleships such as the Arizona and California whose length was 600 feet.
Below are photos of American cruisers of the period 1900-1950. The ship number prefix CA means the ship is a heavy cruiser and a CL prefix designates a light cruiser. The Alaska is a CB, a special designation for cruisers with near-battleship characteristics (but does not mean "battlecruiser").
USS San Diego (CA 6)
The San Diego was originally named USS California but had to be re-named when the battleship California was ordered. Length was 505 feet (154 m). This was only 22 less than the length of the revolutionary battleship HMS Dreadnought that was laid down in 1905, three years after work began on the San Diego/California.
USS Omaha (CL 4)
Cruisers of this type appeared in the 1920s and did not look much like contemporary battleships. Note the spacing of the four smokestacks and that the main guns are well towards the bow and stern. Awkward looking, I'd say. Length was 556 feet.
USS Houston (CA 30)
The Houston was sunk early in World War 2 as part of a multinational force under Dutch command attempting to defend the East Indies from the Japanese assault. A nice looking ship of 600 feet total length (same as first-line battleships when it was commissioned in 1930).
USS Philadelphia (CL 41)
The Philadelphia was a Brooklyn class light cruiser commissioned in 1937. Its overall length was 608 feet, about the same as that of the heavy cruiser Houston. Armament was 15 6-inch guns. Three three-gun turrets are seen towards the bow. Note the the third turret is at the same level as the first, or forward turret. That meant that its guns could not be fired except in broadside.
USS Cleveland (CL 55)
The Cleveland was about the same length as the Philadelphia, but it had only 12 6-inch guns as main armament, the broadside-only turret having been eliminated.
USS Baltimore (CA 68)
The heavy cruiser Baltimore was 673 feet long and looks superficially similar to the battleships North Carolina and Washington.
USS Des Moines (CA 134)
The Des Moines was laid down in May 1945 but not commissioned until 1948. Its length was 716 feet, putting it in the general length range of the the North Carolina and South Dakota battleship classes.
USS Alaska (CB 1)
A more representational view of the Alaska. Something was going on with the forward turret when this was taken. It held three 12-inch guns, but only two are visible and one is raised higher than the other.