Patience. It helps to look at what map you are referring to as each map has some slightly different data. Based on data at the bottom of several of the maps (which lists the specific sources of the map data), the information here is based on original aerial reconnaissance surveys performed during World War II and the early days of the Cold War, and on some Swedish sources that all date from prior to 1950 (for at least most of the maps that I’ve checked). The only real fly in the ointment is a reference to some British Admiralty navigation charts… which technically may have indefinite copyright (the 70 years rule doesn’t apply).

At least as far as these particular maps are concerned, the map itself doesn’t have a copyright as they are works of U.S. government employees, but the sources used to compile these maps may not be so pure and may have used copyrighted sources as a derived work. As the purpose of these maps were for possible use by military units of the U.S. armed forces, little details like copyright purity certainly wasn’t a major concern and getting the information correct was instead the most important detail.

Since these maps have been published almost 60 years ago, on this criteria alone they are technically close to entering the public domain strictly on the basis of having the copyright expire. Formal copyright registration was required for content at the time (copyright was not automatic and had to be requested) in the USA even the source data may be technically in the public domain… but this does get into the fine details of copyright law where some but not all items have entered the public domain due to age.

As to how this applies to somebody not in the USA in terms of copyright… it is right on the edge of being in the public domain anyway. Several of the sources listed have dates before 1940, so the 70+ year rule may apply even outside the USA. In other words, these maps may even be good to use for OSM as something with expired copyright, but it may take a bit more investigation to confirm that, and knowledge of the copyright laws for where you live. It may be a legal source for OSM work, but it is wise to hesitate on this one.