Published in Jumbo Comics #11, Dec 1939 - 6 pages
"ZX-5 battles the Khan's invading Yellow Hordes".
"There has arisen in the mysterious East a mighty vicious ruler - King Genghis". That leader decides that he is in dire need of raw materials he can get from the Isle of Dono which lies just to the west of Chesterland. ZX-5 disguises himself as a captured oriental spy to infiltrate the Khan's headquarters.
Note: there is no mention of any gas!