Seventy-five years after it suffered under deadly and destructive Nazi bombings in World War II, residents of the Welsh town of Swansea are wondering if they’re in a Twilight Zone episode as the eerie air raid sirens have returned … but fortunately not the bombers.

It was called the Swansea Blitz. From the 19th through the 21st of February 1941, Luftwaffe planes from Nazi Germany dropped explosive and incendiary bombs on the strategic port town of Swansea in South Wales. Over 230 people were killed and more than 400 were wounded. This was the deadly end of raids on Swansea that began on June 27th, 1940. That’s when the first air raid siren sounded at 3:30 a.m. The sirens ended on May 7th, 1945, when the war ended. Now they’re back.

The ghostly wails actually began a year ago but their frequency has increased recently. Residents of the Swansea communities of Townhill and Mayhill say they start at 4:30 a.m. and can sometimes be heard until 7 a.m. The siren sounds far away but residents report it’s loud enough to wake a light sleeper – and many of them must sleep light because of the number of complaints the local officials have received about the siren.

While many have heard the sound, there is little agreement on where it might be coming from or what’s causing it. Theories range from pub noise to a factory shift whistle to trains sounding their horns before entering a tunnel to a far-away lighthouse foghorn. All of these have been investigated and none seems to be emitting the ghostly siren from 1941.

Stories of ghost planes, particularly Lancaster bombers, are common in Great Britain – one was reported in August over a treacherous area where numerous planes had crashed. Could this ghost siren be a similar phenomenon in an area that received heavy aerial attacks?

Residents of Swansea are hoping that either the physical cause of the eerie siren is found … or the ghosts still warning of the bombs can somehow find peace.