Newly elected Labour leader Jeremy Corbyn has caused quite the kerfuffle for saying that if elected Prime Minister, his pacifist ideals mean he would not 'push the red button' in the event of a nuclear war.
During the ensuing media deluge, journalist Simon Ricketts noticed an interesting detail about the UK's plan of action in the rather unlikely event of a nuclear war, which he shared on Twitter.
Interesting detail I didn't know, The signal that the UK is no longer a functioning state - Radio 4 cannot be heard. pic.twitter.com/hRJs2tpPBy— SimonNRicketts (@SimonNRicketts) September 30, 2015
It turns out that if armageddon is nigh and the UK is "assumed to be a no-longer functioning state", the signal to Trident submarines around the world is that BBC Radio 4 can no longer be heard.
Indeed - in 2004, a fire alarm at the BBC caused a transmission blackout for 15 minutes, and put the Navy's on-patrol nuclear subs on alert.
If the Today programme, the channel's flagship morning news programme, is not heard for more than three consecutive days, the commander of an on-patrol sub is to open a safe containing handwritten instructions from the prime minister on what to do next.
The Radio 4 check is just one of several that sea captains would have to carry out. But at least the next time you hear The Archers theme tune start, you can rest assured that WWIII hasn't broken out just yet.