When British and American radar development merged

Did the United States develop radar independently or from British designs?

Both countries had their own work, but shared information and joint teams eventually fused the development paths so thoroughly that later systems cannot be assigned neatly to one side.

American radar research predated the closest cooperation, while Britain also brought important designs and experience. As documents, teams, and engineers moved between programs, later results drew on people who had participated in joint work even when a specific project sat outside a formal combined group. The exact boundary therefore requires a detailed chronology rather than a national label.