200 Mt TNT equivalent, four times more than the Tsar bomb. Salted with cobalt to produce cobalt-60, which is what we use to sterilize medical products. Not even spore forming bacterial can survive cobalt-60 radiation.
It would make a coastline devoid of life for centuries.
The torpedo is nuclear powered so can roam the oceans quietly at great depth for many years until activated.
I’d bet there some already out there cruising around.
Such a machine still requires maintenance and upkeep. Out there for years patrolling and waiting to be called upon / activated? Nah...
In my misspent youth we were doing radiation hardness studies to improve spacecraft reliability.
I'd process the chips and a colleague would irradiate them over night to 107 rads using a cobalt 60 source.
One night a black widow spider decided the holder would be a good substrate for a web.
Not only was it quite, quite dead, it crumbled when my friend touched it with his (not zircon encrusted) tweezers!