The poseidon torpedo is designed as a doomsday device. If total nuclear war breaks out, the will create a 2000 feet high tzuanmi and exterminate all human live in the UK that isn´t already in a DUMB when they detonate. They are normaly carried by drones.

The probably will detonate 2 or 3 around the UK and then fire a few RS-28 Sarmat MIRV-15 with 10 - 15 Mts payload at the DUMBs which take around 5 minutes from their silos at Mach 20.

Deathrate in the UK is 99,9999% 5 minutes after the start of the nuclear war so basically nobody in the UK will freeze to death in the nuclear winter.

Lucky island apes.