Residents in the Torpoint and Wilcove areas in the West Country are being sent letters to inform them that an additional alert siren is to be brought into service at HMS Raleigh early next month.

The siren is one of the Devonport Nuclear Accident Alarm Sirens, and is designed to ensure that all those in the 2km pre-planned countermeasure zone – which includes Torpoint and Wilcove – will be able to hear the sirens no matter what the weather conditions.

On Monday November 3 the new siren will be routinely tested at 11.30am for the first time, along with the other seven sirens located in and around Devonport Naval Base, which are tested at this time every week.

Although the existing sirens are already audible in this area, the addition of the new siren will mean the coverage is increased to exceed the minimum legal requirement, and will result in some people – particularly in Millbrook, Antony and St John – hearing the siren for the first time.

Letters will also be sent to people in these areas.

The sirens make a rising and falling wailing sound, similar to the old Civil Defence air raid sirens, and this will last for one minute. It will be followed by the ‘All Clear’ – a steady note – for half a minute.

Captain Base Safety Capt John Binns said: “Safety is paramount at Devonport Naval Base and comprehensive proven plans exist to protect the public in the unlikely event of an accident.

“The Royal Navy has an excellent safety record in the operation of its nuclear submarines, but we keep our plans constantly under review.

“It’s a well-known fact that weather conditions can affect the distance at which sound can be heard. The range of the existing sirens have met and exceeded requirements during the vast majority of weather conditions, but we want to be confident that the siren will be audible to all those who need to hear it regardless of the weather.”

Dependent on wind direction, people who are further afield in St Germans, Polbathic, Sheviock, Crafthole, Portwrinkle, Whitsand Bay, Kingsand, Cawsand and Rame may also be able to hear the siren. Public notices have been placed in newspapers to let these people know.

Information on what to do if the sirens are heard other than at 11.30am on Mondays is available on the inside front cover of the BT telephone directory.

In addition, those who live and work within the 2km zone have been given a leaflet entitled What to do in a nuclear emergency.