Complex sentence: Pure helicopter carriers are difficult to find in the 21st century; the advent of STOVL aircraft such as the BAe Harrier has complicated the classification; the U.S. Navy's Wasp class, for instance, carries 6-8 Harriers as well as 30 helicopters.
Split into simpler sentences: Pure helicopter carriers are difficult to find in the 21st century. The advent of STOVL aircraft such as the BAE Harrier have complicated the classification; the U.S. Navy's "Wasp" class, for instance, carries 6-8 Harriers as well as 30 helicopters.