A nice long short story/novella by one of my favorite authors. Best known for Dominic Flandry and David Falkayn, Anderson wrote of many other protagonists.
This story is one of the better, an American working on a moon of Jupiter, acquainted by radio with a Jovian. Both face a war, deal with it themselves and are able to help each others efforts.
So old that the transmitter they use has tubes, Andderson’s physics are impressive. As I recall, Flandry also has an unexpected visit to Jupiter. 