The Navy and Marine Corps, then, will simply have too few ships, aircraft, and armaments to dedicate to regions of secondary importance. Suitably bulked up, and crewed by mariners who see themselves as warriors as well as the nation’s 9-1-1 force, the Coast Guard would represent the go-to guarantor of security off the United States’ northern ramparts. Heavy Navy and Marine forces would provide a backstop should serious conflict erupt. But Coast Guard commanders would have to hold their own against rival forces until reinforcements arrived.

So how’s that going to work? Polar ventures may require the Coast Guard to square off against a serious military competitor, not just against lawbreakers and the elements. But pummeling enemy fleets, projecting power onto foreign shores, warding off ballistic missiles — business as usual for the Navy/Marine Corps team — are pursuits remote from the Coast Guard’s everyday duties. It may even behoove the service to restore antisubmarine and surface-warfare capabilities dismantled at the Cold War’s end. The Coast Guard fleet need not be a U.S. Navy in miniature, built to rule the waves. But the long arm of U.S. strategy needs battle capacity — not just the light gunnery that now festoons American cutters.

Another task will be to remake the Coast Guard’s organizational culture, rediscovering the half-forgotten tradition of fighting for control of the sea. Command of the sea means wresting control from rival fleets or deterring them through overwhelming firepower. Police duty is something nations do after winning command. Constabulary work like the Coast Guard’s thus differs sharply from combat. Battle demands a different mindset from scouring the sea for drug or weapons traffickers, or from rescuing seafarers in distress following a nor’easter. For the Coast Guard, spearheading Arctic strategy means relearning combat skills last practiced during World War II, while retaining the service’s unique capabilities.