A group of divers have explored the wreckage of a WW1-era Royal Navy submarine - 100 years after it sank.

Dominic Robinson, 54, and a team of 10 dived 74m down to check out the century-old HMS M1 sub 20 miles off the coast of Plymouth, Devon, on Tuesday (19/08).

The HMS M1 was constructed during WW1 but was never used in combat due to fears the Germans would copy its revolutionary design.

Famous for its onboard weapons, the HMS M1 was built with a 12-metre-long gun, firing 12-inch rounds, weighing 50 tonnes.

The sub sank in 1925 when a Swedish ship, the SS Vidar, is believed to have accidentally struck her while she was submerged - leading to the loss of all crew.

It was missing until located by a salvage team in 1967 and was then formally identified by a dive team in 1999.

Alongside a crew of 10 other divers, Dom explored the wreckage to make a video for his YouTube channel.

Dom, from Plymouth, Devon, who is currently in between jobs, said: "The idea of sticking a 12 inch battleship gun on a submarine is so unique. "

"It's like something from steam punk or something made using AI."

"The general view is the collision knocked the gun off the mount, and I think the weight of it has carried it into the sand beneath the main wreckage."

"We were on the water for about three hours - so it's a fairly significant effort for about 25 minutes of diving to look around the wreck. "

"That's the reason only a very small number of divers do this."

Dom claims that diving like this is rare and "well beyond" what many divers will do."

He said: "This is deep technical diving. "

"If you were to go Egypt or somewhere like that they would take you to 20 metres, advanced would be 30 metres, and if you really pushed it 40 metres."

"This is 74 metres - so it's well beyond what 99% of divers will do - but we want to see things that people don't see."

"We don't breathe air when we're down there, we breathe a mixture that has helium in it using a closed-circuit rebreather which recycles the air you exhale."

Dom's YouTube channel - Deep Wreck Diver - has 13,500 subscribers and is dedicated to showing viewers deep shipwrecks.

He said: "I've been involved in some fairly significant discoveries and I take video and put it on the YouTube channel."

"I want to help people understand and the history of these things that are forgotten."

As for his next dive, Dom has his eyes set on finding the USCGC Tampa - a Miami-class cutter that served in the US Navy during WW1.

The boat was still crewed by US Coast Guardsmen after previously being used by the US Coast Guard.

It was sunk by a torpedo from a German submarine in 1918 and only parts of the wreckage were found.

Dom added: "I am part of a team called the Gasperados Dive Team that are searching for it"

"The Coast Guard don't often deploy overseas but in WW1 they sent vessels to the UK and the Tampa was sunk and they lost over 130 personnel on there."

"It's their biggest loss and because of that, if we find it it'll be a really big news story with the Americans."

"We're going to have another attempt looking for that next week."

You can find Dom's YouTube channel here: https://www.youtube.com/@DeepWreckDiver