Unidentified flying objects (UFOs) have caused so much concern in recent years that even Nasa launched a lengthy probe to find out what they were. Now some experts believe the hunt should move from the skies to the sea. The former head of the US National Oceanic and Atmospheric Administration (NOAA) is launching a probe into unidentified submersible objects (USOs) and, in particular, a strange anomaly seen on the seabed off the coast of California. Timothy Gallaudet, a former rear admiral in the US Navy, has spent the past 18 months interviewing dozens of sailors, submariners, military personnel and members of the US Coastguard, all who say they have seen unidentified craft in the water. One incident was filmed by the USS Omaha off the coast of San Diego in southern California in 2019, when a dark-shaped object was seen moving quickly before splashing down into the water. In the renowned Tic Tac incident in 2004, US Navy pilots described an oblong craft shaped like the sweet hovering just above the water off the California coast. Sonar has revealed an unusual trench on the seafloor as if an object has crashed into a ridge and then skidded to a halt. Mr Gallaudet believes that evidence for USOs may be present in the US Navy's acoustic data, but it is currently classified. This week Mr Gallaudet launched a report into the phenomenon alongside the Sol Foundation, a group of academics, military and government officials committed to researching UFOs.