Thursday, January 21, 2021

The M2 – The only submersible aircraft carrier

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History

The Royal Navy’s Monitor class submarines were constructed as WW1 was drawing to a close. With the exception of the M1 class completed in April 1918, they never engaged in military action. The Monitor class was unusual in that in addition to torpedoes, their main armament was a monster gun weighing 60 tons with a 12-inch bore positioned in front of the conning tower. This gun could elevate to 20 degrees, depress to -5 degrees and train left or right by 15 degrees. Their modus operandi was to search for an enemy vessel at a periscope depth of 30 feet and with a suitable target in view, line up on the target with the gun trained at the appropriate angle. With only the last 6 feet of the barrel showing above the surface, the gun was fired and the submarine would dive to a ‘safe’ depth.

The M2, M3 and M4 were completed during 1919 – 1920 and with the Washington Disarmament Treaty of 1920 stating that no submarine could have a gun larger than an 8 inch; the M2 and M3 had their guns removed. The M3 was converted to a very successful experimental mine layer carrying 100 mines in a free flooding casing bolted to the deck that laid them over the stern by means of a conveyer belt. The M4 had the least illustrious career of the class in that with construction on her cancelled during the Armistice, she found herself surplus to requirements. For some reason she was completed anyway and launched successfully down the slipway; whereupon she immediately did an about turn back to the builders yard to be hoisted out and cut up for scrap.

The M2 was also converted to something experimental as her sister the M3 – the construction of a watertight hanger housing a two-seater biplane made it the worlds first and still the only submersible aircraft carrier. The spotter plane was the brainchild of submarine commander Sir Max Horton who was convinced that future power in offensive maritime strategy would lie in submarines and planes, not ships. He petitioned the top brass to combine the two, which they agreed to by building the hanger on the portion of deck that the gun once lay. The small, single prop Parnall Peto seaplane had specially designed folding wings in order to squeeze into the hanger, and was launched by a compressed air catapult along a short length of track. The theory was that the plane would fly around looking for enemy ships, note their position, and then land (on floats) as near to the submarine as possible. A winch attached to the top of the hanger would haul it back onto its rails where it was then slid back in and two sets of watertight doors closed behind it. The submarine would then dive on a course to meet said ships and finish the job with its 8 torpedoes.

The crew was proud of the speed in which they could surface and launch the plane and were constantly trying to break their 12 minute record. It was during exercises in the English Channel on the morning of January 26th 1932 that she dived and never came up again.

She was found 8 days later sitting upright and intact by Navy hardhat divers who reported that both hanger doors were open as well as the 21-inch hatch that connected the hanger to the submarine. Entangled in the wreckage of the plane which had crumpled and been pushed to the back of the hanger by tons of incoming water were the bodies of aircraft technician Leslie Gregory and Leading Seaman Albert Jacobs. The rest of the 58 crew had drowned inside where their remains rest to this day.

It is thought that in trying to improve their record, the hanger doors were opened a few seconds too early in anticipation of breaking the surface. If the access hatch had been closed after the two crewmen preparing the plane for launching had entered the hanger, the remaining crew would have survived. A salvage operation immediately commenced but was called off just before Christmas after 11 months of intense effort by 26 divers logging 1500 dives.

The Wreck today

70 years later the M2 is still sitting perfectly intact and upright on a sand/crushed shell substrate at 110 feet. All access hatches were sealed shut before commencing the salvage attempt so there is no access within. The exception is the hanger itself, which is still open and to most divers is the highlight of the dive. Being current free a considerable amount of silt has settled in there, covering the infamous 21-inch hatch, so it is important to be the first dive group on site before other divers stir it all up to the extent that even the most powerful torch won’t illuminate more than a few inches. Outside the hanger in a recess lying parallel to the rails is a compressed air cylinder not much bigger that the one on your back that provided the initial propulsion to the plane. When the track ends you continue down to the bow until you bump into the hydroplanes and then the 4 outer openings for the 18-inch torpedo tubes, two on each side. Swimming back along the hull you may notice bits of cable and odd shaped bits of metal nestling in the sand, these are not parts of the submarine but discarded/broken bits from the salvage attempts. Continuing past the conning tower, the shallowest part of the dive, you come across the 3-inch aft gun. This is not standing proud to the deck but lying flush with it. When the submarine surfaced it was mounted on a hydraulic platform that ‘popped up’. The stern has another set of matching hydroplanes, two prop shafts and the rudder. The conning tower offers the usual assortment of periscopes by which time you are definitely well into deco and its time to start heading up.

Without stating the obvious there is a big difference doing this site when the visibility is good as opposed to when it is poor – which is most of the time. In poor visibility it can be a little dull as the hull is not dissimilar to a long, smooth, cigar shaped boulder and because the boat is intact there are few nooks and crannies for critters to hide in. With good visibility this is a very, very special dive.

Technical Specifications

Displacement: 1610 tons at surface, 1950 tons submerged

Speed: 15 knots at surface, 9 knots submerged

Length: 296 feet

Beam: 25 feet

Propulsion: Two Vickers 12 cylinder 2400 hp diesels,

Two electric double armature motors – 400 hp each

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