Spike Mason is an agent with the U.S. Naval Intelligence.
We watch his service in the days leading up to but not yet at the entry of America into World War II. The States is helping its allies but still has no found the motivation to break its official neutrality. The Germans are attacking ships everywhere it seems. Japan has expanded throughout the Pacific and rules with a very tight fist. The war lines are being drawn darker every day and America is in constant need of intelligence.
The CIA does not yet exist. Its precursor, the OSS has not been formed yet either. The gathering of intel on the actions and movements of the soon-to-be enemies falls on the shoulders of the Armed Forces and since much of what Japan has accomplished rests with its navy, the U.S. Navy is extremely busy in the Far East.
To that end, we have Mason, an officer (we presume) in the Navy on undercover assignment in the danger zone, taking as his role the job of First Mate aboard a good sized cargo vessel, the S.S. Malibu. It is not clear whether the ship goes wherever Mason feels the need to investigate or whether the movement of the ship just happens to bring Mason to numerous hotspots. Regardless, it seems wherever the Malibu takes Mason, there is something not pleasant happening.
We learn so very little about Mason in the eight short adventures we follow him through. He is definitely good looking. He has wavy hair of apparent auburn color. A couple of panels showing him shirtless reveal that he is in fanstastic shape with considerable muscle which explain how he is able to perform many of the physical maneuvers he has to in order to stay alive.
In the first adventure, he makes friends and get much needed assistance from the Malibu's quartermaster, a husky knucklebuster named Ford. We will see more of Ford's personality over the few adventures available to us and it shows an impetuous fellow who loves to race into trouble, usually but not always making it worse. He is decidedly loyal, though, and obviously once a friend always a friend with Ford.
The Mason of 1940 would definitely not be considered politically correct today as he refers to more than one Oriental he encounters as "coolie" and even better, "slant-eyed scoundrel". Certainly a man of his era. He does love his country and from the looks of things, he loves adventure and danger and he finds both all over the Pacific.