Abstract: The mobile marine drilling structure is of the submersible type for operation in ice-covered waters. The structure comprises a base for placing the structure on the sea bed, a hull extends from the base, and a deck is supported by the hull. The deck is located above the water line for conducting drilling operations. The hull has an internal frame assembly including ballast tanks, and external wall sections at different inclinations to the horizontal to engage and break up the moving ice masses encroaching on the hull. These external wall sections include a plurality of matching polygonal, frusto-pyramidal, apex-up and apex-down walls extending above the base, and two transitional wall sections to provide two inflection points to the hull.