Debbie Ziegelmeyer saw her first UFO when she was leaving a supermarket in Arnold, Missouri, in 1979.

“We were coming out of Kmart and saw two silver metallic discs overhead,” she said. “They were one on top of the other. It was 2.30pm in a bright blue sky. It was all over the local TV news.

“Then they claimed it was weather balloons escaped out of Texas. I don’t believe that. It was so windy that day it was hard to hold the shopping cart, and those things were stationary in the air.”

It led Ms Ziegelmeyer to investigate UFOs. She now heads the Missouri chapter of the Mutual UFO Network.

The organisation has 600 field investigators in all 50 US states and has examined hundreds of thousands of sightings, compiling the largest UFO database in the world. Ms Ziegelmeyer also heads the network’s dive team, which can be dispatched anywhere in the US to investigate underwater sightings such as submerged flashing lights.

The network and the rest of America’s extensive Ufology community is waiting with bated breath for the release of a potentially explosive Pentagon report later this month.

Amid a sea change in approach, the US military is poised to publish what it knows about UFOs, which it now calls UAPs (Unidentified Aerial Phenomena).

Avril Haines, Joe Biden’s director of National Intelligence, will deliver a dossier compiled by the Pentagon’s UAP Task Force to the US Senate intelligence committee by June 25. It is then expected to be made public. It could contain military research on at least 100 key unexplained sightings, including new videos and pictures.

Many see it as an ‘I told you so’ moment in a long, and often ridiculed, quest. “I think the Pentagon’s opening a Pandora’s box. It’s going to spill, and it’s going to spill big,” said Ms Ziegelmeyer.

Leaks suggest the task force has found no evidence of aliens, but has not ruled them out either. The interest in UFOs was reignited four years ago when it was revealed that the Pentagon had a secret probe called the Advanced Aerospace Threat Identification Program (AATIP).

Luis Elizondo, the AATIP director, dismissed suggestions UFOs were advanced foreign aircraft or drones, which are unlikely to be so far ahead of America. But he said: “Is it from here, or from out there? We don’t know. We must keep all options open.”

He added: “We’re just now getting to the point as a government, as a society, that we are accepting the reality that this is real, whatever it is.” However, UFO enthusiasts have been disappointed by government reports before.

In 1968 the Condon Report, which examined 12,000 sightings, concluded they contained nothing of interest and that “further study cannot be justified”.

“I hope the Pentagon come clean with this report,” David McDonald, the network’s 74-year-old executive director and a veteran civilian pilot, said from the UFO network’s headquarters in Cincinnati. “I always thought there would be disclosure about UFOs – but I didn’t expect to see it in my lifetime.” But he added: “I would caution against any true bombshells. I expect they’ll fall back a bit on ‘can neither confirm nor deny’.”

The network’s investigators try to debunk sightings. The most common are silver metallic objects in the sky, and balls of light. More than 90pc are explainable, with causes including aircraft, Venus, the International Space Station and satellites. But about 7pc remain unexplained.

Telegraph Media Group Limited [2021]