When and why did the Royal Navy come to view the expansion of German maritimepower as a threat to British maritime security? Contrary to current thinking,Matthew S. Seligmann argues that Germany emerged as a major threat at the outset ofthe twentieth century, not because of its growing battle fleet, but because theBritish Admiralty (rightly) believed that Germany's naval planners intended to armtheir country's fast merchant vessels in wartime and send them out to attackBritishtrade in the manner of the privateers of old. This threat to British seabornecommerce was so serious that the leadership of the Royal Navy spent twelve yearstrying to work out how best to counter it. Ever more elaborate measures were devisedto this end. These included building 'fighting liners'to run down the German ones;devising a specialized warship, the battle cruiser, as a weapon of trade defence;attempting to change international law to prohibit the conversion of merchantvessels into warships on the high seas; establishing a global intelligence networkto monitor German shipping movements; and, finally, the arming of British merchantvessels in self-defence.The manner in which German schemes for commerce warfaredrove British naval policy for over a decade before 1914 has not been recognizedbefore. The Royal Navy and the German Threat illustrates a new and important aspectof British naval history.