Royal Navy: Nuclear siren due to sound at Portsmouth Naval Base blaring for over a minute - why and when

The alarm will be raised at 9.30am tomorrow morning (June 25) and is known to be heard throughout parts of the city. It lasts for roughly one minute.

Video footage from previous tests shows it can be heard in the surrounding streets and beyond. The statutory tests are part of the Royal Navy’s nuclear accident response plan for the naval base.

Regulations from Portsmouth City Council and Gosport Borough Council outline when they are conducted and the safety plan around them. This is outlined in the local authorities’ nuclear safety plan.

Sirens are sounded three times a year. The routine and regular procedures are carried out on the last Wednesday of February, June and October.

As reported in The News, a previous statement from HMNB Portsmouth 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. Please don’t be alarmed if you hear it.”