High Quality Content by WIKIPEDIA articles! The heavy cruiser was a type of cruiser, a naval warship designed for long range and high speed, armed generally with naval guns of roughly 203mm calibre (8 inches in caliber) and displacing approximately 10,000 tons. While the general mission of the heavy cruiser to act as a fast scout for a battle fleet and protect and hunt down commerce was largely unchanged from the days of sail, its design parameters were dictated by the Washington Naval Treaty of 1922 and the London Naval Treaty of 1930.