Royal Navy: Nuclear siren blares from Portsmouth Naval Base with alert issued - why

The alarm was raised at 9.30am and was heard across parts of the city. The reverberating two-tone noise lasted for one minute.

It was raised as part of statutory routine tests, which routinely carried out on the last Wednesday of February, July and October. These trials are part of the Royal Navy’s nuclear accident response plan for the naval base. It is carried out in accordance with regulations agreed by Portsmouth City Council and Gosport Borough Council.

HMNB Portsmouth issued a reminder this morning ahead of the siren being sounded. They said: “Please note there will be a full test of the Naval Base’s nuclear emergency alerting siren at 9.30am today which may be able to be heard outside of the base.

“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.”