Complex sentence: Unaware of Cunningham's pursuit, a squadron of cruisers and destroyers were ordered to return and help "Pola", formed on "Pola" s sister ships, "Zara" and "Fiume".
Split into simpler sentences: Unaware of Cunningham's pursuit, a squadron of cruisers and destroyers were ordered to return and help "Pola". This squadron was comprised of "Pola" s sister ships, "Zara" and "Fiume".