Air-raid sirens rang out over the British city of Plymouth on Monday as part of a 'major incident' drill at the Royal Navy base there.
Residents received mobile phone text messages from the city council's "Warn and Inform" service as part of the training exercise to test emergency service readiness in case of an incident at the HMNB Devonport, on the picturesque south-west Devon coast.
Those signed up for alerts about the Defence Munitions site at Ernesettle, north of Devonport, or the two fuel terminals at Cattedown on the river Plym also received messages.
The base's dockyard on the Tamar estuary in the west of the city maintains the UK's four nuclear-powered Trident ballistic missile submarines, whose home base is at Faslane in western Scotland.
The site also services the navy's fleet of hunter-killer submarines, and decommissions retired nuclear-powered vessels.
The city's 262,000 inhabitants are used to hearing the siren every Monday at 11:30 am, when the base runs a weekly test of the warning signal to be used in case of a radiation leak.
But this Monday the ominous undulating wail sounded louder than usual — as tensions between the three nuclear-armed powers of NATO and Moscow have hit a historic peak over Russia's special military operation in Ukraine.
The incident drill took place as Russian servicemen and women marched through Moscow's Red Square for the annual Victory Day celebration of the defeat of Nazi Germany in the Second World War. The event is commemorated in the UK as Victory in Europe (VE) day, a day earlier on May 8.
The night-time peace in the 'Ocean City' was disturbed by the sound of guns the previous Thursday, when the army conducted a live-fire artillery exercise on nearby Dartmoor late in the evening.
Other military sites in and around Plymouth include the Royal Artillery headquarters at the historic Royal Citadel fort in the city centre and the Royal Marine 42 Commando barracks in the village of Bickleigh, just north of the city.
The August 2021 Plymouth shotgun massacre took place in the Keyham residential district next to the dockyard, where the 22-year-old shooter Jake Davison worked as an apprentice crane operator for defence contractor Babcock International.