Only a character who begins the game with the Explorer career can be a Submarine Explorer. A character cannot have both the Submarine Explorer and standard Explorer careers.
A character taking this option:
Begins with the Load Bearing ability but does not begin with Big Game Hunter or Language.
Begins with Swimming 1 and Lore (submarine zoology) 1 but does not begin with Medicine 1.
Begins with an Armored Diving Suit (NQ#67, p. 108) and 50 gc but does not begin with a map case or spy glass.