cebreakers are best defined by their primary uses: to break sea ice, to manœuvre in heavy concentrations of pack ice, and to clear channels through which other ships can pass in safety. Ice-strengthened ships, in contrast, are normally cargo transport ships strengthened for use in ice. Heavily reinforced hulls, a sloping forefoot and a ratio of horse-power to displacement of more than unity are characteristics common to both types; the icebreaker being usually distinguished by more powerful engines, higher ratio of beam to length, smaller cargo capacity and such distinctive features as heeling tanks. Icebreakers designed for use in regions other than the Arctic or Antarctic, e.g. in the Baltic or Gulf of St Lawrence, may possess one or two forward propellers, which are not found in polar icebreakers.