Book excerpt: Zimmerman traces the early development of the mission from Britain's initial attempts at technical cooperation in World War I and unsuccessful efforts to restart it in the late 1930s. He highlights Winston Churchill's prominent, yet remarkably inconsistent, role in the story and the often tumultuous diplomatic relations with the Roosevelt administration. Among the secrets Britain revealed was the cavity magnetron, which made microwave radar possible. The Tizard Mission established an effective system of teamwork for Allied technical and scientific cooperation, and it was this teamwork that proved to be a crucial factor in Allied technical superiority. It was also the beginning of the much longer story of Anglo-American scientific and technical cooperation. The Tizard Mission served as a model for the international technical cooperation that continues today in organizations such as NATO.