Embassies and naval attachés extended open-source collection beyond published lists by arranging visits and conversations with foreign services. Japan posted skilled officers to Britain and the United States during the 1920s and 1930s so they could examine what host navies were willing to show and make professional judgments. Britain and the United States used the same method in Japan, while Royal Navy engineers assigned to Germany watched shipyards and maritime infrastructure for signs of rearmament beyond Treaty of Versailles limits. Technical background mattered in these diplomatic appointments because access produced useful intelligence only when an observer could interpret what was visible.
Notable Point · 2:09:01-2:10:27
How naval attachés turn diplomatic access into intelligence
Naval attachés could turn diplomatic access and technical expertise into close observation of foreign fleets, shipyards, and treaty compliance.