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author: behemoth.

about the author: behemoth, from nanjing, jiangsu, began writing in 2014 and has published nearly 700,000 words.

dealing with underwater threats

during world war i, japan joined the allied camp and declared war on germany in order to obtain colonial rights in china and the pacific region. as the german and austro-hungarian navies launched "unrestricted submarine warfare" to block the allied sea routes, the japanese navy was invited by the allies to send ships to the mediterranean theater to perform a series of anti-submarine escort missions, during which time it accumulated certain anti-submarine warfare experience. after the war, the japanese navy conducted a detailed study of its own and the british royal navy's anti-submarine operations during world war i, and believed that submarines would likely sneak attack bases or anchorages where ships were stationed in future wars, so it was necessary to strengthen the anti-submarine defense of ship stationing areas.

in view of this, in 1921 (the 10th year of the taisho era), the japanese navy officially classified anti-submarine net equipment such as emergency nets (a kind of wire net laid near anchorages and waterways, which can be deployed quickly and equipped with mines to attack enemy submarines trying to infiltrate through), capture nets (also a wire net used for anti-submarine purposes, with luminous buoys hung on the net, which can be used to indicate the submarine's track when an enemy submarine is entangled, thereby guiding its own anti-submarine forces to attack) and reference nets (a permanent anti-submarine wire net, which is time-consuming and labor-intensive to set up, but is relatively sturdy) as standard anti-submarine weapons, and proposed to build laying boats specifically for laying wire nets.

figure 1. schematic diagram of the structure of the japanese navy's type 14 capture net

the washington naval treaty signed in 1922 severely damaged the japanese navy for a time, but because the treaty's requirements for small ships and auxiliary ships were slightly looser than those for battleships and aircraft carriers, the japanese navy began to make some efforts in this regard. in 1923, the japanese navy officially included three 500-ton capture net laying boats, two 500-ton standard net laying boats, and one 5,000-ton emergency net laying boat in the new supplementary plan. however, the number and tonnage of ships finally put into construction were reduced compared with the original plan. the number of capture net laying boats was reduced from 3 to 2, and the tonnage was also reduced to 450 tons. the reduction in tonnage was to reduce costs and occupy tonnage share on the one hand, and to improve the maneuverability of ships on the other hand.

the first capture net laying boat was built in 1928, and the second boat was ordered and built soon after. both boats were completed and delivered to the japanese navy the following year. according to the naming convention of the japanese navy, the two boats were named "yan" and "gu" respectively, and the entire class was named "yan" class after the first boat.

small but complete design

although the "yan" class was only a special-purpose ship for "laying" when the budget was compiled, it was continuously added with functions such as anti-submarine, mine-laying, and minesweeping during the subsequent design and construction process, and gradually became a small multi-purpose near-shore (river) combat ship. it is even considered by some naval historians to be the first modern professional minesweeper of the japanese navy. it is also worth mentioning that on march 23, 1929, the japanese navy adjusted the ship type attributes of a series of ships. the original capture net laying boat was adjusted to a second-class laying boat. on may 30, 1931, the original second-class laying boat was abolished, and the "yan" class was reclassified as a laying boat.

the "yan" class adopts a flush deck design, with a total length of 68.8 meters, a waterline length of 65.5 meters, and a draft depth of 2.1 meters. the standard displacement in the initial design is 450 tons, and the full load displacement is 554.3 tons. the middle section of the boat is cylindrical, and the hull is widest near the waterline, and then gradually shrinks upward. as a major feature of the hull, there is a 4-meter-long short shelter deck at the bow. in order to lay capture nets, a bulwark about 600 mm high was added to both sides of the middle of the hull.

figure 2. the yan, which had just been commissioned in 1929, with its bow deck structure in mind

as the main power plant on the boat, the yan class is equipped with two vertical three-cylinder three-expansion reciprocating steam engines driving double-shaft double propellers, and the boilers used are two lu-type coal (carbon) oil mixed-fired boilers. the reason for using this seemingly "backward" and relatively "inadequate" power plant (the maximum power of the three-expansion reciprocating steam engine used in the yan class is 2,500 horsepower) is mainly because the three-expansion reciprocating steam engine has relatively mature performance and low cost, which is suitable for this type of auxiliary combat ships that do not require high speed, and the fuel requirements are relatively low. the boiler can use coal as fuel (the full fuel load of the yan class is 35 tons of heavy oil and 40 tons of coal), which is also a big "good thing" for the japanese navy, which has long suffered from a lack of oil sources. driven by this power plant, the yan class can reach a maximum speed of 19 knots, and a range of 1,200 nautical miles at a speed of 10 knots.

figure 3. sketch of the design of the lu ship's boiler

as a so-called "laying boat", the "yan" class is equipped with a 3-nautical-mile-long capture net for laying tasks. the capture net is usually stored in the storage room at the lower rear of the boat, and there is a capture net setting table on the rear deck. if the capture net laying task is not performed, the boat can carry 80 mines, and there are tracks for carrying mines on the two decks of the boat. in addition, in order to achieve "one boat with multiple functions", the "yan" class is also equipped with strong firepower. the main gun is a 40-caliber 3-year type 80mm (actually 76mm) single-mounted anti-aircraft gun installed on the elevated anti-aircraft deck in front of the bridge. the purpose of this installation is to prevent artillery shooting from affecting the operation of the bridge. in addition to the anti-aircraft gun, the anti-aircraft deck is also equipped with a recovery device for recovering capture nets and mines. in addition, a single-mounted vickers (called "bi-style" by the japanese navy) 13mm anti-aircraft machine gun is installed on the superstructure behind the rear mast. in addition, in order to perform anti-submarine missions, the "yan" class is also equipped with two type 81 mine projectors (i.e. depth charge launchers) and 18 "mines" (i.e. depth charges).

figure 4. a sample of a type 5 mine, which can be laid by a yan-class laying boat.

figure 5. a real 3-year-old 80mm anti-aircraft gun on display at the yushukan of the yasukuni shrine in japan

figure 6. design of the type 81 explosive mine projector

as the war progressed, the allies gradually gained air superiority on the battlefield. in order to improve the survival rate on the battlefield, the japanese navy began to install or upgrade anti-aircraft weapons for various ships from the second half of 1944. among them, the "yan", which had not yet been sunk, replaced the original 13mm anti-aircraft machine gun with a 96-type 25mm multi-mounted anti-aircraft machine gun, and installed a 96-type 25mm single-mounted anti-aircraft machine gun on both sides of the upper deck in front of the bridge, the upper deck behind the chimney, and the rear deck. although the anti-aircraft firepower has been improved to a certain extent, it can only be described as "a drop in the bucket" compared to the allied air force (the final outcome of the boat also proved this point).

figure 7. a twin-mounted type 96 25mm anti-aircraft machine gun installed on land. the magazines scattered on the ground are used by the anti-aircraft machine gun. this gun was the main small-caliber anti-aircraft gun of the japanese navy in the middle and late world war ii.

of course, with japan's ship design and construction capabilities at the time, it was obvious that in order to be comprehensive, it would cost a lot in many places. like many small japanese ships with weapons piled up at the same time, the "yan" class ship also had the problem of too shallow draft and too high center of gravity, which had a serious negative impact on its navigation stability. in addition, the boat's crew quota was 43 people in peacetime, but it would increase to 81 people in wartime, which would inevitably cause a significant reduction in the living environment, thus affecting its sustained combat effectiveness. after the "tomozuru incident" in 1934, the "yan" class hull underwent a round of transformation, including removing the bulwarks on both sides of the hull, shortening the length of the chimney, adding 55 tons of ballast to the bottom of the hull, and adding a ballast keel at 450 mm below the deck. at the same time, the size of the keel at the bottom of the bilge was also increased. after the transformation, the displacement of the "yan" class increased to 557 tons.

if the purpose is to complete the preset mission, the various weapons installed on the yan-class boats are far more than what is needed. in fact, in order to invest limited resources in the arms race, the japanese navy did not hesitate to build each ship into a firepower "hedgehog" with super combat capability, and the yan-class and other heavy firepower small ships are the result of this abnormal idea.

from conquering the east and the west to sinking to the bottom of the sea

soon after the yan class was built, japan entered the track of a full-scale war of aggression. although the yan class boats were not as majestic as various large ships, they were also one of the pioneers of the japanese navy's foreign expeditions. however, in the end, under the attack of anti-fascist forces, all the boats of this class were sunk and finally ended up sleeping in the sea.

the yan

as the first submarine of the "yan" class, the construction of the submarine began on september 17, 1928 in the yokohama dockyard, and it was launched on april 24 of the following year. it was completed and put into service on july 15 of the same year. since then, the submarine has been affiliated with the sasebo naval district and has sasebo as its home port.

after the outbreak of the full-scale war of resistance against japan, due to the shallow draft, strong firepower, and certain minesweeping and salvaging capabilities of this type of boat, the "yan" and the "ou" were incorporated into the chinese fleet of the japanese navy. they salvaged and destroyed the sunken ship blockade line set up by the chinese navy in the middle and lower reaches of the yangtze river and blocked the river surface with naval gun fire to prevent the chinese army from using the yangtze river waterway for transportation. in the battle of wuhan in 1938, the boat became the vanguard of the japanese army's attack on jiujiang, and approached the shore many times to use naval gun fire to support land operations. on the night when the "ou" was hit by the chinese navy, the boat ventured close to the wreckage of the "ou" and dragged it ashore and ran aground.

when the pacific war broke out on december 8, 1941, the boat was assigned to the sasebo naval base, and was later transferred to the 3rd fleet to escort transport convoys sailing in lingayen gulf in the philippines, and was active in tasks such as minesweeping and clearing waterways. since then, the boat has been used to carry out anti-submarine escort missions. on february 28, 1945, the boat arrived at miyakojima near okinawa, and was attacked by a group of us navy f4u "corsair" fighters near miyakojima in the early morning of march 1, and sank into the sea at around 5 o'clock. it was officially decommissioned on may 10 of the same year.

gull

as the second submarine of the "yan" class, the submarine was built at the sakurajima factory of the osaka iron works on october 11, 1928, and launched on april 27 of the following year. it was completed and put into service on august 30 of the same year. after that, the submarine and its sister submarine "yan" were also affiliated with the sasebo naval district and used sasebo as their home port. after the outbreak of the full-scale war of resistance, the submarine was also incorporated into the chinese fleet and entered the middle and lower reaches of the yangtze river with the "yan", and played a fierce role in the battle of the japanese army's attack on jiujiang.

figure 8. the newly built "gull" was photographed in wu port in september 1929. note the equipment on its anti-aircraft deck for recovering capture nets and mines.

on july 16, 1938 (according to the chinese navy's records, and july 6 according to the japanese navy's records), the chinese navy dispatched the torpedo boat wen 93 of the wen tianxiang squadron of the electric mine school to hit the ou, which was anchored on the river near pengze county, jiujiang (according to the japanese records, it triggered a mine laid by the chinese navy). the rear section of the boat exploded and broke and sank into the river, while the front section was towed by the yan and ran aground at wanjia beach. this attack became a rare major victory of the chinese navy's torpedo boat unit during the war of resistance. afterwards, the rear section of the ou was salvaged and repaired together with the front section.

figure 9. japanese naval technicians are inspecting the wreckage of the "gull"

when the pacific war broke out on december 8, 1941, the submarine and the "tsubame" were both assigned to the sasebo naval base. they were then transferred to the 3rd fleet to escort transport groups sailing in the lingayen gulf in the philippines. they were then used for anti-submarine patrols and coastal escort missions. on april 27, 1944, the submarine was sunk by the uss halibut 70 nautical miles north of naha, the capital of okinawa, and was officially decommissioned on june 10.

figure 10. the uss halibut entering the port. the submarine sank a total of 12 japanese warships and merchant ships during world war ii, with a total tonnage of 45,257 tons.