Complex sentence: As Allemand's squadron was estimated to have approximately nine ships, Duckworth initially believed that his enemy was Allemand, possibly accompanied by prizes captured on his cruise, although as he closed with the French it became clear that this was a different squadron altogether.
Split into simpler sentences: As Allemand's squadron was estimated to have approximately nine ships, Duckworth initially believed that his enemy was Allemand, possibly accompanied by prizes captured on his cruise. However, as he closed with the French, it became clear that this was a different squadron altogether.