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http://www.msac.org.uk/wrecks/affray.htm:HM Submarine M1 was developed toward the end of the First World War. Unique in the history of submarine design, she and her sisters M2 and M3 were fitted with 12inch guns from a scrapped battleship. This unique design was born out of the frustration of the submarine service with the relatively short range of torpedoes and their relative expense. These experimental designs were based on the hulls of the ill-starred K-class. M1 was completed before the war ended, but not employed in combat. One theory states that this was because the Royal Navy feared that Germany could copy the design. The U-boat war against British commerce might have taken a grave turn for the worse if such deadly weapons had been employed against Britain's merchant marine. It was, after all, Germany who had made the greatest capital out of the employment of the submarine as an offensive weapon of war.
After the war, the M-Class submarines were used experimentally in developing a range of new submarine technologies. M3 was converted into a minelayer and later scrapped in the 1930s. M2 became the world's first submarine aircraft carrier, carrying a miniature stainless steel-framed seaplane. M2 was also lost in tragic circumstances in January 1932.
M1's first commander was Max Horton, a successful wartime submarine commander who went on to become one of Britain's greatest war leaders when he was appointed Admiral, Western Approaches in 1942. Horton, the navy man who knew submarines intimately, became the killer of the German wolf packs. The M1's 12-inch gun gave her some unique sea-keeping qualities. The gun protected the watch in the conning tower from the worst the sea could throw at them by breaking the waves. Moreover the massive 100-ton weight of the gun turret gave it a fast diving time for such a leviathan. M1 could fully submerge in less than 90 seconds. Once submerged, the 12-inch gun (which was sealed at either end) became buoyant and also gave the vessel excellent handling qualities when underwater. However, when running on the surface, the gun made M1 top heavy and she was not the easiest vessel to control. The 12-inch gun was powerful enough to project the massive shells over 15 miles though a gunnery control system that would have permitted accurate firing was never properly developed. Instead, M1 was intended to be able to surprise its victims by firing at shorter ranges, with only its gun and spotting periscope showing above the surface. At a range of 1200 yards the gun had a totally flat trajectory and could literally be pointed at a target and fired. Not many vessels afloat in 1918 could be expected to withstand the devastating effect of such a bombardment. However, one of M1's drawbacks was that she was a 'one shot deal' because she had to surface to reload, making her instantly vulnerable to counter-attack. Therefore a close range attack, coming to firing depth and submerging was the best way she could be employed. With practice M1 got this routine down to less than 75 seconds.
It must be remembered that M1 was an experimental platform, not a mass-produced vessel. Because of this there were many teething problems with the design. These affected many areas and did cause the submarine a few embarrassing moments. If the hydraulic tampion gear which kept the barrel dry malfunctioned and the gun filled with water, when fired it would shatter.
On two occasions M1 lost half her barrel length when it simply went off in the same direction as the projectile. It is known that on another occasion when this occurred the steel winding within the barrel remained attached to the submarine and to the piece of the barrel that had broken off. The broken section landed in the sea a few hundred yards in front of M1 and effectively anchored her to the seabed. This is the only recorded time that a submarine has dropped anchor by firing her gun! In this case it was the seaman responsible for opening the tampion who had forgotten to do his job. He was most unpopular that evening because a shore leave could not be enjoyed since M1 was anchored out at sea!
A relatively high level of mechanical unreliability is thought to another compounding reason why M1 did not see action during the closing months of World War One. Some historians have suggested that plans had been made to operate M1 on a shore bombardment mission in the Bosphorous, fortunately these plans never came to fruition, possibly because of concerns over her reliability or potential for capture.
