A karmic submarine is a piece of unresolved karma that travels along “under the water” out of sight and out of mind. It doesn’t show on echo location but when the time suits it rises up to the surface. Depending on the nature of the submarine, it may or may not unleash “missiles”. One could term it a skeleton in the closet, a karmic boomerang or something which comes back to bite you in the ass. It may have been suppressed, denied, justified, redacted and explained away. It may simply have been forgotten. But if the submarine decides it will find its way to the surface.
The Indian terminology is karma which ripens and then bears fruit. Fruit can fall from the tree and rot, or it can be picked willingly and enjoyed.
It is difficult to know if one has any karmic submarines, because they can travel at great depth and for very extended periods. Anything might become a karmic submarine. If a challenge presented to one is not faced it may well come back later and say; “Hi, remember me.” One may indeed store up a whole bunch of karmic submarines, a fleet even. I like the metaphor because some of these submarines can “blow up” and turn your world upside down and not just your own world but the world of others too.
It is a bit like secrets. Some secrets don’t want to stay secret, so they push against the container until it pops. Others don’t mind so much and so don’t struggle to reveal themselves. A secret can also be a karmic submarine. An incorrectly attributed paternity could be a nuclear missile armed karmic submarine. I read somewhere that the figure for misattribution is as high as 10%. This kind of thing was the basis for the Jeremy Kyle show.
I have a pet theory, and this is that karma is similar in nature to an overdraft. If one puts off paying off the karma, it accrues interest. The karmic debt simply gets bigger. The longer one puts it off the more likely is the karmic submarine to unleash “missiles”, the destructive power increases. And of course, such destruction is causative of yet more karma.