The Lergravsviken "bicycle-bell" discs (the Åkerberg sighting), Gotland

Gotland, summer 1957. On the island's north-eastern side, just south of Fårösund, lies the bay of Lergravsviken, with the island of Furilden and the air force radar station F13G offshore. On the evening of 5 August, Ernst W. Åkerberg, a police criminal investigator from Stockholm, and his wife Karin had just driven some acquaintances to the couple's fishing cottage by the bay. It was about 10 pm. The sky was starry and cloudless. The moon, five days from full, hung in the south. Not a leaf moved.

Ernst saw "a disc-like object" coming from the north-east, holding course straight towards them, level and at moderate speed. The underside was silver-grey, while the upper part rotated slowly and glittered as it turned. Beneath it was something like a tube, cherry-red, with a steady light and no flames. It passed above the shore less than 200 metres from him. He put its diameter at about 25 metres.

At the water's edge it turned south in a knife-sharp turn of less than 90 degrees. The craft seemed to rise up on its edge and stand there, swaying or fluttering for a moment. In that instant he could clearly see the plate seams and the riveting in the bottom plates. It continued south-east over Fitudden. After about a kilometre it turned again. Then it vanished straight over Furilden.

Then the air moved as a very strong draught rippled the calm water and made the treetops sway violently on the windless night. Immediately afterwards came a second craft. Same appearance. Same course. Same manoeuvres. Only its turn was much tighter. Both were silent, apart from a clicking sound when they were close.

After 30 seconds the whole display was over. Karin said simply: "It's a good thing there were two of us."

The couple reported the sighting to the Swedish Defence Staff, Försvarsstaben. The radar on Furilden had recorded nothing. Its chief of staff, Åke Bernström, said the observation distance was too short. On 17 October 1957, Sture Risberg, laboratory director at FOA 3, proposed research balloons, possibly carrying anti-collision lights. Åkerberg rejected the idea. In April 1959, Capt. Lennart Bunke of the Defence Staff wrote that part of the basis for the evaluation could not be shared with outsiders.

In July 1962, Col. Bror von Vegesack followed up. He reportedly found Åkerberg credible on every point, except perhaps his judgement of altitude. His only comment to the ufologist K. Gösta Rehn was four words. "Vi vet inte vad det är." We don't know what it is.

UFO-Sverige later challenged the balloon theory. It pointed to the still air, the repeated paths, the lack of recovered wreckage, and the reported rivets, rotating top and air movement. Åkerberg himself had no doubts. He wrote that the craft were "real, solid, intelligently controlled spacecraft."

Rehn, who became APRO's Swedish representative in 1958, corresponded with Åkerberg and visited the site with both witnesses. On 13 November 1958 the case was debated on Swedish national radio, P1, with Defence Staff and FOA investigators, Rehn and Åkerberg taking part. Rehn returned to it in his 1966 book De flygande tefaten.

Today UFO-Sverige lists Lergravsviken among the eleven cases in its archive that still have no explanation. In 2018, Clas Svahn called it one of the most interesting UFO sightings from Gotland. His write-up ends plainly. "And we still don't know."