So, you fire your hard to intercept missile, which probably can be detected all the way out at Jupiter, and everyone in your country is dead because the counter strike gets there about 60 minutes before your missile hits it, and every single country it flew over on the way is out for vengeance?
Who says the launch can be detected? For all we know, only the failures were detected.
Be even if, are you going to nuke Russia just because they launch it? In theory they could fly for months. They may even be able to recover again. Russia could have an entire flock circling in a remote area of the world. That alone doesn't justify a nuclear retaliation any more than an SSBN patrolling under the Arctic ice cap does.
MH370 didn´t have a 100MW or so beacon shouting "look at me, shoot at me" during its whole flight.
Again, who says it can be tracked instantly when operating normally?
Even if they could, would the tracking be able tell if there was a formation of multiple missiles fast enough for anybody to react accordingly?
France would probably vaporize where the missile came from for just sending it over its territory.
Turning the entire area of France below it into the next Chernobyl or Fukushima in a spat between Poland + the US and Russia? Doubtful.
Yeah. If you want to be sure that every time someone detonates a nuke in or near a harbor everyone automatically assumes you did it and may retaliate before figuring out where the Plutonium came from, then a nuclear Torpedo makes absolute sense. The "beauty" of ballistic missiles is that it is pretty hard to not know where it came from.
The Americans have placed large parts of it's missile shield on ships. Nuclear torpedoes would take out an Arleigh Burke with ease.