MANY DIVERS WILL HAVE HEARD OF, if not actually dived, the famous wreck of HMS M2. This British submarine sank off the south English Dorset coast and, since her rediscovery nearly 40 years later in 1970, has been a port of call for thousands of divers enjoying summer diving out of Weymouth.
 At a friendly depth of 32m, M2 lies upright and intact, her bronze conning tower covered with jewel anemones and the crane that would once have lifted her seaplane back aboard still obvious on her foredeck.
 M2 was the first submarine to carry such a seaplane. Her conversion to an aircraft-carrier was completed in 1927, before which time she carried a monster 12in battleship gun forward of her conning tower, in the same way as her sister-subs M1 and M3.
 It was during peacetime, in 1932, that M2s crew made a fatal error. Her hangar doors were opened too early, flooding her hydraulic systems and making her unstable. So she followed M1, which had sunk seven years earlier, to a watery grave at the bottom of the English Channel.
Within eight days the Royal Navy had used sonar to locate M2, though M1 remained undiscovered.
 The M-class British submarines, developed towards the end of World War One, were unique. All three were fitted with 12in guns from a scrapped Majestic-class battleship and, using the Dip Chick method, would rise suddenly to the surface, fire a round and dive again - all in around 30 seconds!
 Although top secret and experimental at the time, it was thought that no merchant vessel would survive a hit from these new weapons. The M-class submarines were completed before the war ended, but never used in combat, as the Navy feared that Germany, which dominated submarine warfare, might copy the design and wreak havoc.
 On 12 November, 1925, M1 went missing while on exercise off the Devonshire coast. Her loss remained unexplained until the collier Vidar entered Vatara Harbour in Stockholm almost a week later.
 Vidars crew had reported colliding with an unidentified submerged object off Start Point in the Channel, and her damaged bows revealed traces of a rare paint that had been used on M1.
 Navy divers and survey vessels searched for the lost sub for a month before abandoning hope of locating her. Over the next 66 years, stories of M1s location emerged occasionally, but no evidence was produced. It seemed certain that she was lost in deep water.
 Then deep waters started to become more accessible, as mixed-gas diving gradually became mainstream.
 The first claim to have discovered M1 was made by legendary salvage operator Silas Oates. I have often read about this character and his exploits, but his M1 tale was put to rest when the sub with the monster gun was found in water far deeper than he had claimed.
 In 1991, Royal Navy survey vessel HMS Bulldog carried out a sonar survey of the area in which M1 had been lost, and discovered several submarine-type wrecks. Nelson McEachan, who today works for the UK Hydrographic Office, was on that survey team and told me its members were 99.9% sure that one of these vessels was the M1.
 With no diving or ROV inspection, the report was inconclusive, but this was the most positive sounding so far.
Nelsons position was finally verified on 18 June, 1999, when Weymouth skipper Graham Knott relocated the wreck along with submarine researcher Innes McCartney, his wife Patricia, Chris Hutchison and the late Keith Morris.
 This small team became the first to dive to and see M1 in the 74 years it had been on the seabed. The wreck was McCartneys Holy Grail, a giant sub in home waters, and the long hours of research he and Knott had undertaken had finally paid off. The team returned with video evidence that the legendary M1 had been seen again.
 I will never forget hearing their triumphant news, as their cell-phone signals came back into range. I had not joined them at sea, as I was in hospital to witness the birth of my first daughter.
 But on 2 August I joined Chris Hutchison for a further investigation. The M1 wreck sits on a silty seabed at 75m, with a least depth of 66m to the top of the conning tower. It is almost upright, 5m proud of the seabed with a slight list to port, and almost intact except for that huge 60 ton gun turret and operating mechanism. This has fallen on the port-side seabed only 2m from the main hull,
 The gun barrel was obviously knocked off when Vidar collided with the sub, and has been picked up on sidescan sonar some distance from the wreck.
 In front of the silhouetted conning tower is the area where the gun turret fell, leaving the circular mounting on which it sat. The mounting ring appears twisted a fraction to port, and closer study reveals how M1 met her fate.
 Rather than sitting on the pressure hull, the mounting ring passes right through it, so as the Vidar knocked off the gun, water would have flooded the interior of the shell-room. With no air to blow the ballast tanks, it would have taken the vessel straight to the seabed.
 So the gun was M1s strong point and, it seems, at the same time its weakness.
 Forward of the turntable, there is extensive damage to the top of the hull, and a V-shaped gash in the hull. Above, in the conning tower, an open hatch on the starboard side perhaps indicates an attempt made by the crew to escape. Behind the tower is another, much larger, hatch. Again, it is open.
 Today, a large trawl-net drapes this relatively small conning tower, although you can still see the helm boss through the net, plus other interesting fixtures.
 The conning tower would have accommodated only a handful of men, and the cut-out footholds they once used to climb from the decks below are evident among the white anemones that cover almost the entire wreck.
 Further trawl-net hangs high between the conning tower and the stern. Chris Hutchison reported that a bronze hatch towards the bow is also open, enabling divers to view the crews chinaware, still stacked neatly on its shelves.
 The props are intact, but once again draped in net, this time monofilament.
 The outer hull casing shows signs of rotting, and in many areas has gone completely, leaving the underneath framework visible.
When good conditions prevail, the 300ft-long M1 provides a magnificent spectacle, but with these dives under my belt, I felt the urge to do a comparison dive, and joined one of the charter boats out of Weymouth.
 M2 lies in Lyme Bay, a relatively short trip around Portland Bill. Its spectacular bow with knife-like razor edge, at the northern end of the site, provides the strongest comparison with the M1.
 Visibility of 15m is not uncommon here in summer, and you can see the wreck disappearing into the distance.
 M2 sits upright, and the tracks that once ran the seaplane off the deck can be followed easily from the bow to the hangar. The hangar door went during the salvage attempt and divers can see inside. Look hard enough and you can see the concrete once laid to seal up the hatchways leading below. One or two huge conger eels have made this home.
 I was told by skipper Graham Knott that at one time the recovery jib used to recover the seaplane could be seen on the wreck and on the sonar from above, but it was lost six or seven years ago, probably trawled off.
The conning tower is intact, and as spectacular as you might expect. This is the best place to ask your skipper to shot.
 The periscope tubes can still be seen and, moving aft, I saw a small gun in a recessed position inside the hull.
 No diver can miss the hydroplanes both fore and aft and, approaching the stern, I saw the propshafts and their mounting brackets, though the props were nowhere to be seen.
 It seems they were taken by a salvage team, long before the 1986 Military Remains Act came into being. The seabed is littered with brittlestars and wire hawser cable left from the salvage attempt.
 Divers venturing off the wreck about 150m to the south-west will discover one of the huge flotation tanks that once lifted the wreck clear of the water before being lost again. In summer, as well as the usual light covering of dead mens fingers, M2 hosts schools of pollack, wrasse and the odd lobster.
 In poor visibility, the wreck can be quite moody, but if you want to dive a submarine that looks like a sub, this is it.
M1 and M2 are the only examples left of this type of submarine, as M3 was scrapped in the 1930s. If you havent dived either, try the approach Chris Hutchison and I took, which was to dive them in numerical order!
 Both are protected by the Military Remains Act, which states that divers are not allowed to enter, tamper with or remove anything from the site. Visiting divers should be aware that many servicemen lost their lives in the sinking.

  • M1, Wrightys Charters (www. wrightys-charters.co.uk) or Deep Blue Diving (www.deepbluediving.org); M2, Weymouth Diving (www.weymouthdiving. com) or Skin Deep (07971 977595)

  • Sister-sub
    Sister-sub M2 in action as her plane is launched from its hangar at sea
    Seen alongside fleet battleships, M1s 60 ton, 12in gun gives some idea of her potential firepower
    US wreck-diver Mike Boring joins English divers as they prepare gear for an early-morning M1 dive
    Italian diver Antonello Paone made the journey too
    the dive-boat Seeker picks up divers after a dive on M1
    the mounting ring on which M1s 60 ton gun once sat
    The M1 appears to be breaking down with age. Here machinery on top of the wreck can be seen.
    The gun-mount turret mechanism for M1s 60 ton gun, which now lies on the portside seabed from the wreck.
    Hidden today by snagged trawler net, M1s propeller can only just be seen