I can't immediately find a source with a date, but I'm pretty sure using submarine to mean undisclosed happened before Paul Graham was born.
Re:The Milk Situation
by portlander12345 on Sunday March 15, 2020 @02:14AM
(#22581700)
OP used the term specifically to refer to PR-generated articles in prestige media like the NYT, which was probably a direct allusion to Graham’s essay.
[1] http://www.paulgraham.com/submarine.html