Along with Sword of Samurai, Devils of the Deep was to be yet another Fighting Fantasy game on the C64 from US Gold according to http://pdd.if-legends.org/ldp/bdp.html.
This game in particular was to be set in Atlantis and we presume would have been by the same developers using a version of The Quill.
However, like the others this never quite surfaced. Compared to the other games planned or released, this never really got a mention and its only the above website which seems to know of the games.
As a result its still very early days, but an entry none the less!
More information needed…