Yes, it's an intimidating term, I think. It sounds evil. The British dreadnaught changed the era. Some later BBs are referred to as "super dreadnaughts" built closer to WW One.
Some argue the Iowa class is more of a battlecruiser than battleship. I don't get too hung up on such distinctions.
The Lexington and Yorktown were built on battlecruiser hulls.
The Iowa Class were generally referred to as Fast Battleships. They were MUCH more well armored than a typical Battlecruiser.
Off the top of my head simplified explanation of the terms:
Cruisers:
Cruisers were smaller and generally faster than Battleships. The Washington Naval Treaty did not explicitly define "Cruisers" but they were de-facto defined because the Treaty limited the major ships (Battleships, Battlecruisers, and Aircraft Carriers) and the "other" were limited to not more than 10,000 tons each and with guns not larger than 8".
Battleships:
Battleships were the heavyweight fighters. They carried large guns and sufficient armor to stand up to hits from equally large opposing guns. To wit, the concept of "balanced Battleship" existed even before Dreadnaught and demanded that a Battleship should have sufficient armor to withstand a hit from a gun equal to it's own. They were huge, extremely well armed, and extremely well armored.
Battlecruisers:
Battlecruisers were more-or-less a compromise between Battleships and Cruisers. They had Battleship guns but only Cruiser Armor. Ie, they were NOT a "balanced" ship and could NOT withstand hits from guns equal to their own. However, they were MUCH faster than contemporary Battleships. They had Cruiser speed. The theory here was that Battlecruisers could outrun anything they couldn't pulverize and pulverize anything they couldn't outrun.
Fast Battleships:
This was a much later innovation. The Battleships of the WWI era could only make about 20 kn. For example, the American Colorado Class had a top speed of 21 kn. Three were completed shortly after WWI with the fourth (Washington) being scrapped in accordance with the Washington Naval Treaty of 1922. The next class of US Battleships was the North Carolina Class which did not come into service until two decades later, just before WWII (the two ships were commissioned in April and May of 1941). The North Carolina class had a top speed of 28 kn. Top speeds of US BB's starting with Colorado:
- 21 kn Colorado Class (Colorado, Maryland, West Virginia, and the never completed Washington)
- 28 kn North Carolina Class (North Carolina, Washington)
- 27.5 kn South Dakota Class (South Dakota, Indiana, Massachusetts, Alabama)
- 33 kn Iowa Class (Iowa, New Jersey, Missouri, Wisconsin and the never completed Illinois and Kentucky)
- 28 kn Montana Class (None ever laid down but five were planned: Montana, Ohio, Maine, New Hampshire, Louisiana)
Fast Battleships like the 33 kn Iowas effectively rendered all Battlecruisers obsolete but it wasn't possible to get that kind of speed along with large guns and sufficient armor on a Treaty-limited Battleship. The South Dakota's more-or-less complied with the then existing treaties so they were limited to around 35,000 tons. The Iowa's were fully post-treaty ships so they were built without regard to such limitations and displaced nearly 60,000 tons at full load (New Jersey actually did displace a full 60,000 in it's Vietnam era tour).
The US laid down several Battlecruisers during WWI and, as you noted above, Lexington and Yorktown were converted from Battlecruisers to Aircraft Carriers during construction in order to comply with the Treaty. The US also built the Iowa Class Fast Battleships and a rather curious class of "Large Cruisers" known as the Alaska Class. The US Navy has consistently discouraged referring to the Alaska's as "Battlecruisers". Also, the Alaska's were never named using the "CC" designation reserved for Battlecruisers but they also didn't get the "CA" used for cruisers. Instead they were "CB-1, CB-2, and CB-3" (Alaska, Guam, and Hawaii). Also note the names. They were not named after states like Battleships nor after Cities like Cruisers. Instead they were named after territories which seems like it fits between?
The Alaska's were officially "Large Cruisers". They displaced about 30,000 - 35,000 tons which is as large as Treaty Battleships (well, it would have been except that basically everybody was cheating during the treaty era it was just a question of by how much). They had 12" guns so much smaller than contemporary BB's (16+) and armor somewhere between a Cruiser and a Battleship along with 33 kn speed.
The Alaska's made very good Carrier escorts which was all that really mattered by the time they came online but it has often been pointed out that for the price of one Alaska Class Large Cruiser the US could have built several Baltimore Class Cruisers and as Carrier Escorts it is pretty hard to argue that one Alaska is better than three Baltimore's. The Alaska's were designed to deal with Japanese ships that were planned (or believed to be planned) but by the time they were commissioned the Japanese Navy had been almost completely converted into Coral Reefs by US Carrier Aircraft so their intended use was gone before they were available.
