Many British cruisers served on the Northern Patrol to prevent neutral merchant shipping from running contraband goods through the blockade to Germany, and to shadow any German warships trying to break out into the Atlantic.

This was a heavy commitment in both men and ships, in waters notorious for bad weather and bitter cold in winter. To relieve cruisers for more urgent duties with the Fleet or on distant stations the Admiralty reverted to a device they had used in the First World War. They requisitioned fifty large liners on the outbreak of war and armed them with six inch guns to serve as Armed Merchant Cruisers, or AMC's. The AMC was hardly ideal for the job as her towering sides made her a good target, her capacious passenger decks made an excellent fire-trap, and her lightly plated hull offered only enough resistance to a shell to trigger its fuse.

Yet two armed merchant cruisers, the Jervis Bay and the Rawalpindi, fought actions against German capital ships which equalled the deeds of any regular cruiser. As the war progressed the Admiralty paid off the AMCs and converted them to troopships or amphibious transports. Nothing emphasises the value of the cruiser in World War II more than these examples of attempts to provide the qualities of a cruiser when one was not available.