28 September 2021

Vigil finale: How do submarines communicate?


With over seven million people tuning into the gripping finale of BBC One’s submarine-based drama Vigil on Sunday, audiences might be wondering what life is like deep beneath the waves.

Most UK households are increasingly reliant on good phone and broadband connections to communicate, so it’s hard to imagine being on a vessel with little means of contacting the outside world.

The communications we use on land obviously don’t work in the same way for submarines underwater, but radio technology does help crews to communicate with other vessels and land bases.

How it works

Submarines use very low frequency radio waves for communication when submerged. Radio waves are absorbed quickly by seawater, and the deeper a submarine travels, the more water those radio waves need to get through. Very low frequency radio waves can only travel a few tens of metres. Submarines can deploy buoys equipped with antenna closer to the surface to enable them for communication when they are deeply submerged.

These very low frequencies only support narrow bandwidths, so only allow for low levels of data to be carried. This means normal voice communication isn’t possible, and only very slow data can be supported – submarines may use Morse Code, for example.

Submarines are sometimes equipped with on-board devices that can connect to the internet with higher data rates, including via satellite, but these can only be used when submarines rise to the surface. As seen on the show though, Navy submarines might not want to do this, as it could leave them vulnerable to detection. Ofcom’s Spectrum team works with the Ministry of Defence to help keep the UK Navy’s communications running smoothly. Our spectrum engineers help to troubleshoot problems vessels might experience with radio frequencies, such as interference.

This is another example of how important spectrum is for connecting critical services, every day.

There is more information about how Ofcom manages spectrum in the UK on our website.

What is spectrum?

You can’t see or feel radio spectrum. But any device that communicates wirelessly needs spectrum – such as televisions, car key fobs, baby monitors, wireless microphones and satellites. Mobile phones use spectrum to connect to a local mast so people can make calls and access the internet.

Why does Ofcom manage spectrum?

Only a limited amount of spectrum is available, so it needs to be managed carefully. Certain bands of spectrum are also used for different purposes. For example, mobile companies use different parts of the spectrum to TV companies. So, it needs to be managed to prevent services interfering and causing disruption to people and businesses.

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