This book is about Cold War electronic reconnaissance with an emphasis on missions undertaken by the United States, United Kingdom and Sweden, but a number of other nations, including France, are part of the story as well. Sweden’s location on the Baltic Sea gave it a dominant role in Baltic area defence matters and in preparations for a war that luckily never broke out. The authors have benefited from access to previously classified material in American, British and Swedish archives related to airborne SIGINT activities over the Baltic 1946 to 1990. Swedish material relates not only to Swedish Air Force operations, but to all foreign flights and activities that were observed by Swedish radar surveillance and intelligence agencies in the Baltic area. By combining and comparing the documents from these sources, it is now possible for the first time to achieve a better understanding of what really took place in the sometimes dangerously crowded skies over the Baltic Sea during the Cold War.