Wrong answer 
,
Cutters are another name for patrol boats of various sizes. Corvettes are alittle larger and naturally have somewhat increased weaponery. Next comes Frigates, then Destroyers, Cruisers, Battlecruisers, Battleships and Carriers (BS and CA are the same level). After that theres the Dreadnaught 
The reason the US navy dont worry about corvettes is that they are designed to take out subs, thats basically their job, a cheap sub killer. US have 
of Frigates that do the same job, so they have no need for corvettes, and the patroling duties are done by the coast guard with cutters, and the coast guard dont need corvettes because they dont go sub hunting..... atleast officially 
I would like to know where you got your information, because according the Navies of various nations, Jane's, etc. it is not entirely correct
at all. "Cutter" is most certainly NOT just another name for patrol boat. Patrol Boats are MUCH smaller vessels usually consisting of a crew of one officer and six enlisted crewmen, or less, are short range vessels, and can not stay at sea for any long period of time. Shoot, most types of PB's do not operate far from shore. Although Cutters do perform the same missions, your definition is not only an over simplification, it is also quite misleading. This is especially true for your definition Corvette. You claim that it is used exclusively for submarine hunting and nothing can be further from the truth. The nations of Italy and Spain, for example, do not use Corvettes for that mission
at all, rather it is used to patrol shipping lanes within their territorial waters near major ports. Both nations also use Corvettes for customs and security inspections of cargo vessels before they entire their ports. Other nations, such as Norway, also use Corvettes for search and rescue, a mission
identical to US Cutters. If you actually look at some examples of foreign Corvettes and American Cutters, you will actually see that their displacement is roughly the same, armanent is often very similar, and the actual missions performed are identical. While it is true that some nations use Corvettes to perform missions that the Americans use Frigates for, this does not in any way mean that Corvettes are closer to Frigates in design. This is almost exclusively the result of cost vs. available resources vs. security priorities.
You also seem to suggest that CG Cutters being used to search for subs is some kind of big secret. It isn't. During the Cold War the #1 line of defense against Soviet ballistic missile subs in US territorial waters, and not far beyond, was the American Coast Guard. Using their Cutters, search planes, and helicopters in conjunction with US Navy assets, the CG performed anti-sub sentry duty for over three decades. This is common knowledge.
In addition, unless you are talking about several Sci-Fi franchises, Dreadnaughts are
not the largest class of vessels. They are actually an older class of Battleship that sailed during a time when "Battleship" was just a common identifier for Heavy Cruisers and Dreadnaughts and was not actually a class. This did not come until new warships far exceeding the displacement and firepower came into being during the naval arms races of early and mid 20th century. Wanderer's answer to that is spot-on. There's
of smart folks on this board, I'm sure any of them can give the same info. Dreadnaughts, in some Sci-Fi,
are massive vessels that combine the ability of the Battleship, and the Carrier. If this is what you mean, try to be more clear please.
Contemporary class designations include: Frigate
FG and various subtypes; Destroyer
DD and various subtypes such as DDn for Destroyer, Nuclear; Light Cruiser
CL, and again various subtypes, such as Guided Missile, Light or Heavy Cruisers; Heavy Cruiser
CA; Battlecruiser
CB, this is a very misleading class, and many nations have their own definitions. The first Battlecruisers were essentially much faster Heavies. Some nations converted their old Dreadnaughts to CB's by installing more powerful engines, better guns, etc. To some nations, such as the Soviet Union during the Cold War, a CB was a class of ship between a CA and a Battleship. I personally prefer to use that definition when CB's applied to FS; Battleship
BB; Carrier
basic designation is CV for fixed wing carriers, and CH for rotary wing or VTOL carriers. Most US carriers are "CVN's" for Carrier, Fixed Wing, Nuclear.I left out a number of details. I'm sure one of the great folks here can fill them in if they wish. I'm bored and got home late and there's something good on the tele, so that's all from me.
