Complex sentence: The design evolved from aircraft carriers converted for use as helicopter carriers (and as a result, are often mistaken for conventional fixed-wing aircraft carriers), but includes support for amphibious landing craft, with most designs including a well deck.
Split into simpler sentences: The design evolved from aircraft carriers converted for use as helicopter carriers (and as a result, are often mistaken for conventional fixed-wing aircraft carriers). Modern ships support amphibious landing craft, with most designs including a well deck.