How many broad types of twentieth-century navy were there?
Short answerBrown-, green-, and blue-water are useful starting labels, but logistics, expeditionary reach, ship capability, and national requirements make every navy distinct.
NotesThe familiar progression runs from brown-water riverine forces through green-water littoral forces to blue-water oceanic fleets. Those labels are useful only at a high level because two navies in the same category may have very different endurance, logistics, aviation, and expeditionary capacity. Raw escort counts are especially misleading when one list includes ships far smaller and less capable than another navy's frigates. Auxiliaries can determine whether a nominally powerful force sustains operations far from home, while a smaller regional navy may be suited to a different set of national requirements. In practice, each navy reflects a unique compromise between geography, missions, industrial capacity, and what its political system will fund.