Complex sentence: The total squadron consisted of some 1,980 men (crew plus infantry), of which only 188 would survive a voyage which was to prove one of the most terrifying, challenging, heroic and adventurous circumnavigations of the globe ever completed.
Split into simpler sentences: The total squadron consisted of some 1,980 men (crew plus infantry), of which only 188 would survive the voyage. It was one of the most terrifying, challenging, heroic and adventurous circumnavigations of the globe ever completed.