"The Stolen Radium"
Major Thorpe (writer and artist), George Tuska (pencils and inks), Pierce Rice (pencils and inks)
Published in Jumbo Comics #16, Jun 1940 - 8 pages
The leader of neighboring Regorvia, Herman Gottler, has invaded Chesterland. Worried that the nation's supply of radium will fall into enemy hands, ZX-5 is sent to West City where the stockpile is to keep it safe or destroy it. He discovers it has already been stolen. Before he can do anything about it, he is captured and sent to a POW camp where Josoix orders his execution.
Here are the pages I have of it.