A team of divers has explored the wreckage of the WW1-era Royal Navy submarine HMS M1, more than a century after it sank off the coast of Plymouth, Devon.

Led by 54-year-old Dominic Robinson, the group descended 74 meters beneath the surface on Tuesday (August 19) to film the submarine for Robinson’s YouTube channel Deep Wreck Diver, which has more than 13,000 subscribers.

The HMS M1, constructed during World War I, was never used in combat but was revolutionary for its time, built with a 12-meter-long battleship gun capable of firing 12-inch rounds. In 1925, tragedy struck when the submarine was accidentally rammed by the Swedish vessel SS Vidar while submerged, killing the entire crew. The wreck remained missing until discovered in 1967 and formally identified in 1999.