Royal Navy: Loud nuclear siren to sound at Portsmouth Naval Base - when and why

The alarm will be raised at 9.30am on Wednesday morning (February 25). it has been known to be heard throughout parts of the city and outside the base. Blaring sounds usually last for just over one minute.

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The siren is sounded to perform statutory tests of the Royal Navy’s nuclear accident response plan for the naval base. A Royal Navy statement previously said: “It is a statutory requirement to test the alarm three times a year and this test is being conducted in agreement with Portsmouth and Gosport local authorities.

“The two-tone siren will be sounded for one minute for the test.” Routine and regular procedures, outlined by Portsmouth City Council and Gosport Borough Council, state that the siren is sounded three times a year.

This is carried out each year on the last Wednesday of February, June, and October.