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

The alarm will be raised at 9.30am tomorrow morning (October 29) and has been known to be heard throughout parts of the city. It lasts for just over one minute.

The statutory tests are part of the Royal Navy’s nuclear accident response plan for the naval base. A social media statement from Portsmouth Naval Base issued last year said: “Please note there will be a full test of the Naval Base’s nuclear emergency alerting siren at 9.30am, 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.”

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 on the last Wednesday of February, June, and October, each year as a routine procedure. Video of the siren produced this summer shows how loud the alarm is at the base.