Complex sentence: The "Valiant" s had long Navy careers: "Warspite" was decommissioned in 1991, and "Valiant" in 1994, due to cracks being discovered in her primary to secondary cooling system.
Split into simpler sentences: The "Valiant" s had long careers with the Royal Navy, with "Warspite" being decommissioned in 1991. The nameship, "Valiant", was decommissioned in 1994 due to cracks being discovered in her primary to secondary cooling system.