1931 Draining the dry dock

Just some minor wrinkles (old seagoing term for picky details, as in the navigator's vade mecum Lecky's wrinkles (in practical navigation))

Dry docks are pumped out (as you properly put it a bit lower down), not drained (they'd have to be above sea level for a drain to work). The 'water tight gate' is known as a 'caisson' usually pronounced, with a wild irrationality only British navalese seems to manage, 'cassoon' though occasionally (but not by 'old navy'!) 'kayson'. The local blokes attending to the 'beams', which are properly called 'shores', were colloquially known as 'dockyard mateys' or just 'mateys'. The 'gang planks' are called 'brows' usually in the singular with a more specific qualifier, 'port forward brow', 'quarterdeck brow', etc. (from the Old Norse 'bru' meaning a bridge) and occasionally (though not in the RN) gangways.

The shores that were being placed last, like the one you show being hauled into place, had to go in last because they were not supposed to take a lot of strain, since their ends are between the thin walls of the outside ballast tanks, which don't have much structural strength. All the ships would have had their sides marked up to make sure that shores were placed symmetrically on each side and, on the ship, up against a frame and not against unsupported plating.

The ship moored on the West Wall (that had two arms, west and east, either side of the dock entrance) from which the photo was taken was HMS Cumberland, which had arrived in HK on 12th March, 1928. She was back in UK for a refit in 1929-30, getting back to HK in April 1930. The Cumberland, back from a visit to north China (where she'd been pranged by the Butterfield and Swire steamer Poyang on 28th December (damaging the bow)) was on the West Wall from 28th Jan to 23rd Feb. She left for sea for an exercise on 24th Feb. The West Wall was c.750' long and a County Class cruiser 630' loa, so she covered the lot. Supposing she was berthed bows west (which seems to have been most usual), the part of the ship opposite the dock gate (and slightly left of centre), would probably have been the platform at the base of the port crane beside the aft funnel.

The big crane was a 30 ton electric travelling jib crane (i.e. driven by electric motors) built as order No. 4404 (drawing no. 1156) by Cowans, Sheldon & Co. of Carlisle in 1924 (drawings are held at the Cumbria Council archives). Cowans Sheldon built most of the HK naval dockyard cranes, including the Fairbairn steam cranes (the chaps that look like a quarter of a circle) that were the first installed in 1905. The company was taken over in 1961 and by 1987 only a design office remained in Carlisle. As Grace's Guide puts it, "The giant sheds were demolished and beefburgers are now fried where once some of the world's greatest cranes were made." (See also https://www.tulliehouse.co.uk/collections/cowans-sheldon-and-co-cranemakers) 

In 1926, two years after the crane for Hong Kong had been built, Cowans, Sheldon built the largest floating crane ever built at that time. The 150 ton lift monster, for the dockyard in Nagasaki, was used to build the warships that were to give so much trouble fifteen years later. Oh, the wonderful joys of the free market.

A larger, 50 ton lift clone of the HK yard crane was installed at the Sturrock graving dock in Cape Town during WW2. It is still there and really keen Meccano buffs can build a model (https://runnymedemeccanoguild.org.uk/gallery/sections/members,michael-ad...) 

Worth noting that the Odin class boats had a completely differently shaped bow to the 'L' class, the latter's being like that of a surface ship (flared) and the former's sloping down towards the water - not that that's easy to spot and made very much more difficult by the placing of the anti-piracy 'Gwulo' watermark. (The National Maritime Museum in Greenwich has the original starboard elevation and general arrangement plan drawings of the Osiris.) The two boats in the pic are the same class and conform to the plans of the Odin class - what I can see of the bow fits the specs.

The SCMP for Feb 17, 1931 answers the question of the second submarine's identity, noting that in dry dock that day were HMS/Ms Oswald and Osiris with HMS Sterling. The previous day the Sterling had not been docked. The two submarines were evidently in for a major overhaul (you can see the aft topedo tubes seem to have been removed on both) and had gone into dock between 15th Jan (when they went into dry dock with HMS Cornflower). The Cornflower undocked on 28th Jan and the Sterling dry docked on 17th Feb. Sterling came out of dock on 5th March and was promptly replaced by HMS Bridgewater. The Bridgewater and the S/Ms finally undocked between 14th & 18th March, the latter after two months on the blocks but, given the shuffling around, never having any major work done that prevented them from floating when changes were made as between the Cornflower, Sterling and Bridgewater. Obviously the dockyard team was pretty slick at flooding up, shifting vessels around, and then pumping out, settling them on their blocks and shoring up. Tracking down all the movements - and realizing that for the docking of the Cornflower, Osiris, Oswald and the undocking of the Cornflower and docking of the Sterling the Cumberland had to get out of the way - there was an amazing amount of shuffling about. 

The Osiris, Oswald, Otus and Odin had arrived with the Medway on 9th August 1930, so the first refit was after they'd been in HK six months. They'd all left UK in late May, but there had been a six week delay in Malta because of defects in the submarines that had to be fixed...or perhaps not entirely fixed.

Best, StephenD