Infogrames released a much more basic and limited version of this game, in France, in 1988, entitled "Bob Morane: Ocean". I'm not sure if there was a PC version or not.
The European version of Project Neptune is called Operation Neptune. One difference in the European release is that the player character is called Bob Morane (the same as in the earlier version of the game). In the US release, the player character is called Rip Steel.
The game documentation comes in a "Top Secret" folder, as a series of memorandums, reports and other documents.