Breathless coverage of the revelations that the National Security Agency (NSA) has been tracking allied foreign leaders aside, spying on allies -- even friendly ones -- is nothing new in international politics. In the mid-sixteenth century, the pious King Philip II of Spain and the pope kept tabs on each other as they prepared for the sailing of the Spanish Armada against Britain. The reason? The pope thought the king indecisive, and the king believed that the pope was hedging his bets.
Centuries later, in early 1917, the British government wanted the United States, then neutral, to enter World War I on its side. According to Keith Jeffery, the official historian of MI6, London’s intelligence service, the British used a “whole range” of overt and clandestine methods to gather intelligence and run influence operations. For example, thanks to its secret surveillance of a U.S. transatlantic cable, MI6 learned of a German plot to win Mexico’s allegiance by promising the country a chunk of U.S. territory. Masking its source, MI6 delivered the alarming news to U.S. President Woodrow Wilson and thus nudged the United States toward a declaration of war.
Signal intercepts were not the United Kingdom’s only source of intelligence on its hoped-for ally: Sir William Wiseman, a British intelligence operative, penetrated the White House by earning the trust of Wilson and his closest adviser, Colonel Edward House. While also running illegal covert operations on U.S. soil, Wiseman gathered intelligence on Washington’s opinions about the conduct of the war, its preferences for how some postwar territorial issues would be resolved, and its strategy for the Paris Peace Conference.
The United States returned the favor by collecting the communications of friendly powers during the peace negotiations. Even as Wilson publicly espoused open diplomacy, his closest advisers had hired the cryptologist Herbert Yardley to run a signal and cipher unit that gathered intelligence on the other delegations. Yardley provided a similar service at the Washington Naval