The task of examining Britain's effort to maintain strategic dominance despite logistical dependence upon Franklin Roosevelt and the United States begins with an assessment of Britain's shipping situation. As Britain's Chiefs of Staff (COS) acknowledged in the memoranda quoted above, British hopes for continued resistance and eventual victory in the Second World War would depend upon an ample flow of imported supplies, particularly those routed through the West Coast ports. Britain simply had to import vital foodstuffs and raw materials. For example, two-thirds of its food, 90 percent of its bauxite, and 95 percent of its petroleum had to come from overseas suppliers. Britain had to maintain sufficient merchant shipping capacity to move those supplies. Only thereby could this island state's oceanic commerce sustain war production.

Britain would veer perilously near failure in the endeavor to maintain enough merchant shipping capacity to sustain imports, escaping only through logistical dependence upon America. What factors affected Britain's ability to provide enough merchant shipping capacity? Enemy action posed the most obvious threat to wartime supply.