Complex sentence: The "Essex" class was a class of aircraft carriers of the United States Navy, which constituted the 20th century's most numerous class of capital ships with 24 vessels built in both "short-hull" and "long-hull" versions.
Split into simpler sentences: The "Essex" class was a class of aircraft carriers of the United States Navy that constituted the 20th century's most numerous class of capital ships. The class consisted of 24 vessels, which came in both "short-hull" and "long-hull" versions.