Arcade (VIC Dual)
Released in US: September 1977
This game has unused graphics.
Blow up subs, but don't sub the subbed subs for subs.*
*Feel free to replace every instance of "sub" with "submarine sandwich" or whatever your region names them.
An unused marker that's stored with the destroyer and submarine markers data. Either this icon was put in as a joke, or there were supposed to be whales that the player could destroy with explosives.
(Source: Original TCRF research)