Travel the US and abroad to hear first-hand accounts from seasoned, decorated police officers who have had unbelievable, but substantiated, UFO encounters.

In 1990, a pilot flying his small plane off Catalina Island spotted an object just below the surface of the water which enveloped his plane with a bright light, freezing his controls.

Has the US military derived various forms of technology, including stealth technology, from downed UFOs?

For years, people have claimed to have had direct, personal contact with aliens. The team tracks down some of those who claim to have had such encounters.

This episode chronicles several close encounters with alien abductees who have been held captive, probed, examined, and had objects implanted in their bodies.

In 1947 an unknown object approaching US air space at great speed and a civilian craft out of El Paso were heading towards each other when they disappeared from radar.

The UFO Hunters travel to Stephenville, Texas, to investigate multiple reports of strange lights in the sky.

The team examine a declassified US Department of Defence report which analyses an alleged encounter between a fighter pilot and a UFO.

The team travels to Sedona, Arizona, long known for strange phenomena, to interview witnesses to unexplained sightings of lights and objects in the sky.

The team analyses incredible NASA footage of reported UFOs, and interviews former NASA employees who allegedly witnessed cover-ups firsthand.

In 1980, British and American soldiers stationed at NATO/RAF bases near Rendlesham Forest observed a mysterious object in the sky. Was there a cover-up about these events involving the military and intelligence agencies?

Believers say that the sighting of 12 UFOs on radar triggered a military alert at Edwards Air Force Base in California on Oct. 7, 1965.

An Air Force team is in a deadly plane crash after investigating a Washington state UFO sighting reported a week before an incident in 1947 Roswell, N.M.

Series examining UFO sightings, alien abductions and government cover-ups, beginning with an investigation into multiple sightings of bright lights in Illinois in 2004.

The team finds new evidence concerning the strange booms and menacing orange lights that panicked people in Indiana in 2008, upending theories that it was a military jet.

Investigation into a huge pulsating light spotted in the sky near Ohio in 1994. A radar operator describes what he saw, explaining he had "never seen anything move so fast".

Experts investigate the alleged crash of an alien craft in Texas in 1897, debris of which was reportedly thrown down a well while an alien body was buried in a local graveyard.

The team uncovers rare footage of floating giant triangles hovering over cities. Could these strange sightings be extraterrestrial in origin?

The team investigates disturbingly similar stories of alien abductions from two different countries before tracking down some potential proof in Mexico.

The team investigates rumours of human-alien genetic experiments reportedly going on deep below the New Mexico desert in an underground base.

Upon learning about a connection between the UFO phenomenon and the Third Reich, the team travel to Germany and Poland to investigate.

From 1987 to the early 1990s, Florida was inundated with UFO sightings, while 90 miles away at Guantanamo Bay, USOs (Unidentified Submerged Objects) were seen rising out of the ocean.

The team examines the most compelling examples of UFO relics available, including a unique and other-worldly piece of metal in Missouri.

The team investigate eyewitness reports of cattle slaughter allegedly caused by UFOs, and are hot on the trail of a recent mutilation case.

The team investigate the highly secretive underwater testing facility AUTEC, said to be used by the US Navy for weapons testing and underwater research.

UFOs are the biggest mystery of our time and somebody - or something - seems determined to keep it that way.

Area 51 is considered the ultimate top secret facility, but there is another military site, known as Area 52, where strange phenomena have been witnessed for 10 years.

There's a growing phenomenon of alleged UFO sightings known as 'Orbs'. Witnesses who see the orbs also report having dreams, premonitions and a deep fear.

The team sets out to try and uncover the American armed forces' 'first response' to UFO encounters.

Ever since Roswell, observers have noted that UFOs allegedly appear in locations that are already full of secrets and mystery: namely, weapons labs. The question is, why?