Research Thread - IJN vs. Allied ASW

[joea]

Ok, if we are going to tweak things to get a more realistic and historical I thought it might be useful to compare and contrast ASW doctrine and development between the IJN and the Allies (RN, RCN and USN).

Here are two links to start:

http://uboat.net/allies/

http://www.combinedfleet.com/

REPORTS OF THE U.S. NAVAL TECHNICAL MISSION TO JAPAN

http://www.fischer-tropsch.org/primary_documents/gvt_reports/USNAVY/USNTMJ%20Reports/USNTMJ_toc.htm

We could look at:

1) Pre-war ASW doctrine

2) Wartime experience and development

3) Technology and weaponary

Just to start. Please add in your 2 cents.

Japanese ASW weapons and stats

http://www.navweaps.com/Weapons/WAMJAP_ASW.htm

Japanese radar

http://www.combinedfleet.com/radar.htm

Japanese Sonar and ASDIC

http://www.fischer-tropsch.org/primary_documents/gvt_reports/USNAVY/USNTMJ%20Reports/USNTMJ-200B-0343-0412%20Report%20E-10.pdf

[clayton]

I forgot the sight, but I remember reading the actual patrol reports from the different fleet subs in the Pacific. I think that would be invaluable.

[FAdmiral]

American Sub Doctrine at the start of WW2 in the
pacific was to protect the BB TFs and sink enemy warships (same as Japans). Adm Nimitz changed all that when he
figured that Japan, like England, was an island nation and needed to ship in all the resources to sustain itself. So he
used the German approach to go after the merchant & tanker ships (or convoys later) doing the resupply. I think that
caught Japan off-guard in relation to what American Subs would be doing till at least late in 1942 when they finally
started to catch on....

JIM

[Gizzmoe]

Stickied!

[tater]

As you can see from the IJN ASW link, they had no real doctrine at all, frankly. Not in relation to merchant shipping in particular.

It's important to remember that DCs are, um, explosives, and they sit on the deck, unprotected. For a ship that saw its role as using them as offensive weapons against their submarine foe, they are critically important, and ready for quick use. For a navy whose doctrine was that DDs were offensive platforms with capital ships as the foe, not submarines, DCs on the deck are unarmored bombs waiting to be detonated by just about anything heading their way.

For a feeling of IJN ASW doctrine, I really suggest buying The Japanese Merchant Marine in World War II by Mark Parillo. Unfortunately it is out of print. He goes into great detail regarding the timeline of IJN ASW activities.

[joea]

Thanks Tater, I've spent some time this evening searching for info on IJN anti-sub detection devices. Nothing on sonar or hydrophones or their capabilites, nor how they compared to Allied ones. :-?

I got info on radar, that's a start, we need to find out more about ASW air support or lack of it.

[Bilge_Rat]

some thoughts:

The IJN never developped an effective radar, but IJN crews were trained in night fighting and had superior binoculars and optics to the allies. In 1942 around Guadalcanal, there were many instances when IJN crews would spot allied surface ships at night 3-5 minutes before the japanese ships showed up on US radar.

IJN crews were very highly trained at the beginning of the war and this gradually tailed off as replacement and green crews came in. At the beginning of the war, there were many instances where US subs would attack a convoy or warship only to then be subject to a ferocious counterattack from IJN fleet destroyers.

However, the IJN never developped an effective ASW doctrine since they viewed ASW work as being "defensive" and beneath them. Therefore there were many flaws in their attack doctrine, they tended to set their depth charges at shallow setting (100 feet I believe), since they thought allied subs could not go much deeper. They also broke off depth charge attacks sooner than allied escorts, allowing many allied subs to escape.

As the losses mounted, Japan instituted a proper convoy system at the end of 1943, but never with the same level of dedication as the allies.

I have a couple of reference books at home if you are looking for specific info. WW2 naval actions in the pacific has always been one of my area of interest. I'll see what I have on IJN sonar and depth charges.

[tater]

The IJNAF would have used various seaplane units to provide air cover over island bases. This would be usually a Mavis (H6K) unit. These planes should be spotted as singletons. They might bomb and report. Meanwhile (early in the war) there would be little forthcoming in terms of air attack. Hunting subs is not like hunting a CV battle group. The sub is either destroyed in the bombing, or it dives, and the added aircraft are a wasted effort.

So in a realistic H6K radius around a jap island, have a chance of a Mavis attack. Later there might be other floats (CA floats, notably). G4Ms (Betty) might also get tasked for this role sometimes as well, maybe G3Ms (Nell) as well. Seeign fighters anywhere but very close to land seems wrong, they would not have been used, it would be more of a random encounter for the fighters... "there we were, when we looked down and saw a sub. I made a hand signal to my chutai, and we strafed until the sub dived, then RTBed."

The air side of SH4 is pretty silly right now, frankly.

The IJNAF also did not have VS units as part of CV air wings. They had VB, VT, and VFs. They'd obviously likely fly some ASW patrols, but it would have to be with Kates or Vals since most Zeros didn't have radios. Regardless, I'd expect to almost always see any non-maritime patrol aircraft in 3s snce the fundamental unit of japanese aircraft organization was the 3-plane Chutai.

On a slightly related note, the IJN CVs need a mod to remove the aircraft from the flight deck. IJN doctrine had all aircraft embarked below in the hanger spaces. PLanes were fueled, amred, and warmed up below decks (mostly). This allowed the flight deck to be clear for CAP take off and landing ops. This is the opposite of USN doctrine which embarked all aircraft on deck, and only struck them below for maintenance. USN CVs should have all the planes forward (jam-packed), or all the planes aft (also jam packed). So the IJN CVs would look more realistic without planes on deck unless you happen to be shooting while they are about to launch a strike (in which case it should be steaming into the wind at flank speed).

Back to escorts, I think it will be a tough task to find good info on their doctrine regarding the prosecution of submarine contacts. It's easier to look at the general scheme of things instead. In terms of mods, this would mean making the escorts act a little more like USN/RN DD/DEs (notably minus radar) , but reducing the number of such escorts. It is plain from Parillo's book, as well as Evans and Peatie's excellent book, Kaigun, that until 1943, there was zero attention to the submarine issue at all. There were literally 2 officers in the entire fleet tasked with escort organization, and that was in addition to other stuff on their plates. 2 part-time officers to conduct all navy organization regarding escort activity. Otherwise, escort duty was the bailiwick of the regional admirals. Taking DDs away from the Combined Fleet was not looked upon well.

Also, while not strictly an ASW issue, the japanese subsidized a "scrap and rebuild" policy of the merchant marine. This required 4000 ton ships that could make 13.5 knots. Many such ships were built. As a result, the merchant captains were against convoys themselves since moving at the speed of the slowest would often result in a group of 13.5 knot ships having to wait for a single slowpoke. Independant shipping was the result. Actually, another factor came into play there. the japanese couldn't offload ships very efficiently. So a convoy would saturate a port's ability to deal with the cargo. So cargo carriers tended to like showing up, unloading, then leaving without having to wait. They needed to, too. The japanese required more shipping than they actually had, it needed to be at sea as often as possible.

From the SH4 standpoint, I think that the radar needs fixing, the uber-intel of units radioed to the player needs to radically drop, and subs need to be forced to patrol around mostly for isolated ships. Note that in the main sea lanes (Japan-Truk, Japan-Singapore, and to a lesser extent Japan-Palau) the IJN would patrol. Not escort usually (before '44), but patrol.

[AntEater]

It seems the IJN did have operational (and effective) radar from 1943 on, but it was inferior to US radar.
Generally it seems to me the IJN became gradually more effective in ASW during WW2, but could not capitalize on this experience in 1944 because of the general slaughter that ensued on land and in carrier battles.
Similarly to the italians, who totally bungled ASW in 1940/41 but got quite good at it in 1943.
Keep in mind most USN subs were lost in 43/44, and losses to planes only started in 1944/45 when the IJN apparently had airplane based radar.
Sadly SH4 has totally useless river gunboats, but no Ukuru class escort ship or Tomozuru class torpedo boat.


Regarding the CVs, the regular scouting duty done by VS squadrons in the USN was done by the carrier attack planes in the IJN. The Aichi D3A (Val) dive bomber was awkward to handle on carriers since it had non folding wings. The B5N (Kate) torpedo bomber had better range, DF equipment and a third crewmember to help with navigation. At least on approach to midway, one carrier always had flying duty comprised of attack planes on ASW patrol.

[Redwine]

Really interesting...

http://www.navweaps.com/Weapons/WAMJAP_ASW.htm

Allied the most used allied Depth Charge was the 420lbs. one, with a lethal radius between 4.3 filled TNT in early and middle war times, and 7m filled with Amatol/Minol in later war times.

Japanese only has 220lbs, Depth Charges with a rate of sink of 1.9m/s.
This means the lthal radios must to be much samaller than above for 420lbs.
Sure they needs to explode so near the hull, almos the half of the above values for 420lbs, may be between 2m and 2.5m.

Only after 1943, japanese developed a 357lbs, Depth Charge, with a rate of sink of 3m/s.
The lethal radius for them must be between 3m and 4m only.

Ingame defalut settings are a random value between 4.5m and 40m.... a very unrealistic value...

I changed the lethal radius to a more moderated values, now i am using a random value between 4.5m and 10m, wich is too biger than in real life.

4.5m is about the double of the real life value, and 10m is about 4 times the real life value.

Plus i reduce the sink rate from 5m/s default down to 3m/s wich is near 60% more higher than in real life (1,9m/s)

It is similar i done for SH3, works fine.

[joea]

Added the giant USN technical report on Japanese Weapons from 1945 , including a link to Japanese sonar. :up:

[Bilge_Rat]

Radar - based on my reading, Samuel Morison's History of U.S. naval operations in ww2 and Clay Blair's Silent Victory, IJN ships never carried an effective radar, certainly not one that ever had any practical effect in any battle, does anyone one have solid evidence to the contrary?

Depth Charges - as Redwine pointed out, the IJN never developped heavy depth charges like the allies.

ASW capabilities - If you read through the documented encounters between the IJN and U.S. subs troughout the war, the IJN was at it's most effective at the beginning of the war. All their destroyers were equipped with sonar and they knew how to use it. However, from my reading it appears they never developped the team tactics used by allied escort, rather each escort would attack on its own. The IJN ASW effort became progressively worse as the war wore on and the crews became greener.

U.S. intel - The U.S. Navy broke the japanese codes before the war and were reading japanese messages throughout the war. They kept close track of the movements of japanese ships and U.S. subs were often dispatched to intercept specific warships or convoys, so the superb intel we get in SH4 is based on fact, although it may require some tweaking.

RDF - The japanese had a very effective Radio Detection Finding network set up before the war which allowed them to keep close tab on allied warships. The U.S. knew this from intercepted messages, which is why U.S. subs used their radios sparingly, although I don't know how this could be integrated in the game.

[tater]

Radar - based on my reading, Samuel Morison's History of U.S. naval operations in ww2 and Clay Blair's Silent Victory, IJN ships never carried an effective radar, certainly not one that ever had any practical effect in any battle, does anyone one have solid evidence to the contrary?

One, Samuel Eliot Morison is a good overview, but it's the USN take on things from right after the war. Little or no japanese sourcing. That said, the IJN did have some effective radars later in the war, but there were bloody few of them. Convoy escorts (usually NOT fleet DDs) just didn't get such gear.


ASW capabilities - If you read through the documented encounters between the IJN and U.S. subs troughout the war, the IJN was at it's most effective at the beginning of the war. All their destroyers were equipped with sonar and they knew how to use it. However, from my reading it appears they never developped the team tactics used by allied escort, rather each escort would attack on its own. The IJN ASW effort became progressively worse as the war wore on and the crews became greener.

While true, the problem is that the escorts in question were virtually always escorting other warships, or merchants that were part of an invasion fleet. They knew how to use the tools they had, but they had no operational doctrine for ASW at all, really. No overall plan. Interestingly, their fleet CAP was similar. Throw some Zeros up, and they'd fly around looking for AAA fire to alert them to contacts (since few carried radios) and hunted on their own. This is in stark contrast to radar tracked, CIC tasked CAP in the USN.

U.S. intel - The U.S. Navy broke the japanese codes before the war and were reading japanese messages throughout the war. They kept close track of the movements of japanese ships and U.S. subs were often dispatched to intercept specific warships or convoys, so the superb intel we get in SH4 is based on fact, although it may require some tweaking.[quote]

Quite true, though depending on the year the number of convoys may be too high IMO.

[quote]RDF - The japanese had a very effective Radio Detection Finding network set up before the war which allowed them to keep close tab on allied warships. The U.S. knew this from intercepted messages, which is why U.S. subs used their radios sparingly, although I don't know how this could be integrated in the game.

Excellent point. Does sending a contact report attract attention? Any IJN warships should be alerted by their sigint section...

tater

[Bilge_Rat]

I was looking through the japanese ASW section of the report of the U.S. naval technical mission to Japan that JOEA linked to:

http://www.fischer-tropsch.org/primary_documents/gvt_reports/USNAVY/USNTMJ%20Reports/USNTMJ-200I-0244-0309%20Report%20S-24.pdf

it seems to contain all the info we need on IJN ASW capabilities and tactics to properly tweak the game.

[panthercules]

I'm not sure how much info can be gleaned/reverse engineered from the reports about the sinkings of US subs, but this site (http://www.csp.navy.mil/) has what seems to be some really good info about all of the US subs lost in WWII. I've just started playing around with stuff there, but it was interesting to learn that of the 25 US submarines lost through the end of 1943, 11 appear to have been lost to enemy surface ships and only 3 to enemy air attack (and one of those was while in port, though another 3 are attributed to mines but could possibly have been unreported air attacks), with 6 or 7 having been losts in accidents and 1 to an enemy sub. In terms of what sort of results to aim for in tweaking, it would seem that surface vessels should be about 2-4 times more dangerous than airplanes, at least during the first couple of years of the war.

[PeriscopeDepth]

I forgot the sight, but I remember reading the actual patrol reports from the different fleet subs in the Pacific. I think that would be invaluable.
Browse through web sites of WWII subs, many of them have all the war patrol reports for that particular sub. For example, the Batfish's website is where I got my sig from: http://www.ussbatfish.com/batfish-main.html. A few years ago when I was way into SHI I think I spent a sleepless night reading as many war patrol reports as I could find. It's fascinating reading actual play by plays of real WWII sub's Pacific War patrols.

Excellent point. Does sending a contact report attract attention? Any IJN warships should be alerted by their sigint section...
There is an RDF sensor in the game's data files. Should be pretty easy to test, just sit off the coast of Japan and send repeated messages.

PD

[heartc]

I've just started playing around with stuff there, but it was interesting to learn that of the 25 US submarines lost through the end of 1943, 11 appear to have been lost to enemy surface ships and only 3 to enemy air attack (and one of those was while in port, though another 3 are attributed to mines but could possibly have been unreported air attacks), with 6 or 7 having been losts in accidents and 1 to an enemy sub. In terms of what sort of results to aim for in tweaking, it would seem that surface vessels should be about 2-4 times more dangerous than airplanes, at least during the first couple of years of the war.

I'm pretty sure this stems mostly from the relatively early advent of the SD radar set on USN subs, which often gave them enough time to dive before the airplane could get a visual on them.

[Bilge_Rat]

I pulled out some raw numbers from silent victory:

1942-there were 350 patrols resulting in 180 ships sunk (725,000 tons), including 2 cruisers and 6 submarines. 7 U.S. subs were lost, 1 in port to an air attack, 3 by grounding, 3 sunk. An average of 8 torpedoes were fired for each sinking.

1943-there were 350 patrols resulting in 335 ships sunk (1.5 million tons), including 1 escort carrier and 2 submarines. 15 subs were lost. An average of 11.7 torpedoes were fired for each sinking.

1944-there were 520 patrols resulting in 603 ships sunk (2.7 million tons), including 1 BB, 7 CV, 2 CA, 7 CL, 30 DD and 7 subs. 19 U.S. subs were lost. An average of 10 torpedoes were fired for each sinking.

[panthercules]

I pulled out some raw numbers from silent victory:

1942-there were 350 patrols resulting in 180 ships sunk (725,000 tons), including 2 cruisers and 6 submarines. 7 U.S. subs were lost, 1 in port to an air attack, 3 by grounding, 3 sunk. An average of 8 torpedoes were fired for each sinking.

1943-there were 350 patrols resulting in 335 ships sunk (1.5 million tons), including 1 escort carrier and 2 submarines. 15 subs were lost. An average of 11.7 torpedoes were fired for each sinking.

1944-there were 520 patrols resulting in 603 ships sunk (2.7 million tons), including 1 BB, 7 CV, 2 CA, 7 CL, 30 DD and 7 subs. 19 U.S. subs were lost. An average of 10 torpedoes were fired for each sinking.

Interesting numbers (actually lost 17 subs in 1943, according to the site I noted above, but two of those were accidents not involving combat against Japanese forces, which would get to the 15 number noted above). This sort of backs up someone's (Beery's?) observation about SH3 that it was really a u-boat ace simulation rather than just a sub sim - I don't think most folks would really play the game for long if it accurately simulated an average of 1 sinking every 2 patrols or even 1 per patrol, as the numbers above would suggest. However, I don't think most folks would play it for long if you always get record-breaking totals every time out either, so I hope the modders can reach some happy medium that will give you a reasonable chance to replicate the results achieved by the ace skippers or maybe even surpass them a bit, but make it a real challenge to do so.

[tater]

Some of it is ASW, some aircraft, and some should simply be sensor mods in terms of reducing the kill counts for people to a sane level (that is still fun). Having the radar pick out contacts when you don't have radar, etc, is kind of crappy. As is having contacts called out when the periscope is up---that's what I'm for, looking through the periscope, lol.

I'd think that having contacts harder to find would go a long way. The air issue is another interesting one. As I posted, the loadouts are absurd for the jap planes. OTOH, having air as a serious threat will keep skippers submerged during the day which should reduce detection ranges---even for periscope mounted radar since LOS is still a concern.

tater

[panthercules]

Radar - based on my reading, Samuel Morison's History of U.S. naval operations in ww2 and Clay Blair's Silent Victory, IJN ships never carried an effective radar, certainly not one that ever had any practical effect in any battle, does anyone one have solid evidence to the contrary?

Theodore Roscoe (in United States Submarine Operations in World War II) states that IJN surface ships didn't start getting radar (10cm) until early 1943, and that they started with their capital ships (BB Hyuga getting the first, apparently) and didn't really begin equipping escorts with radar until September 1944 (p.211).

Roscoe also indicates that airborne radar was only installed in Japanese medium bombers in the Fall of 1943, with a special squadron of radar equipped (but obsolescent) planes formed for convoy escort duties in December 1943, with widespread deployment of radar-equipped planes not coming until Fall 1944 (p.211). He states that the Japanese airborne radar, when it was used, was reportedly able to detect a sub at a range of 12 miles, and toward the end of the war they were making a significant number of night contacts on subs. Japanese doctrine supposedly called for radar to be used only at night or in low visibility, prefering visual searching by day - not sure how that would/could be reflected in the game. They also sometimes turned their radars off, even at night, fearing Allied radar detectors would give away their positions.

Roscoe indicates that shipboard radar detectors were introduced as early as 1942, and most escorts were equipped with them by the end of 1944. These detectors apparently had directional capabilities. Radar search receivers were not installed in Japanese aircraft until late 1944 (and even then not in many ASW aircraft), but these were not actually capable of "homing in" on Allied submarine radars.

Roscoe did indicate that the RDF network was good enough to allow the Japanese to fix a sub's position on just about any radio transmission (other than perhaps ones used in short range between subs in line of sight) - within a box about 100 miles square. Apparently, this might allow for some re-routing of traffic away from areas where subs were thus known to be operating, but was of limited use operationally in terms of letting the IJN dispatch surface vessels or aircraft to intercept the sub (unless the sub was close to an airbase or port during daylight when it broadcast).

There's a lot more info in the Roscoe book about things like aircraft equipped with what sound like MAD devices (able to detect submerged submarines by flying over them at low altitude), merchant armament, depth charges etc. - not sure how "objective" or accurate the information is (first printed 1949, and still tinged with some less-than-PC attitude), but it's an interesting read in any event.

[PeriscopeDepth]

As is having contacts called out when the periscope is up---that's what I'm for, looking through the periscope, lol.

tater

This is actually a feature so that you can run with the scope up at a high TC and get contacts called out still. I understand it isn't great when you're the one looking through the scope, but oh well.

PD

[joea]

Great thread here: http://www.subsim.com/radioroom/showthread.php?t=110840

Links here:

http://groups.msn.com/HistoryWarPolitics1775/navalhistory.msnw?action=get_message&mview=0&ID_Message=41339&LastModified=4675538329078913248


Japanese ASW Efforts


In their overall war plan, the Imperial Japanese Navy strategists overlooked the U.S. submarine fleet. In the 1930s, as the new fleet-type submarines were replacing the older S-boats, Japanese Foreign Minister Shidehara declared, "The number of submarines possessed by the United States is of no concern to the Japanese inasmuch as Japan can never be attacked by American submarines." His view appears to have been shared by the IJN's leaders, who failed to see that an island is a body of land completely surrounded by a submarine's favorite element. Their underestimation of the submarine is a strategic error difficult to comprehend. In World War I, Japan's naval observers had seen the U-boat blockade bring England to the verge of defeat. Again, in 1940, the undersea fleet of Nazi Germany all but sank the UK. The similarity of Japan's insular position to that of the British Isles is apparent on any map. Certainly the U.S. Navy was aware of the analogy.

By the beginning of 1943, the U.S. submarine force knew just about what to expect in the way of Japanese antisubmarine measures. The Japanese Grand Escort Fleet, organized convoying, and aircraft equipped with radar and a magnetic airborne submarine detector were still in the future. However, the basic ingredients of the Japanese antisubmarine effort were in the pot.

Japanese ineptitude in this field of undersea warfare was, of course, recognized by the submariners and exploited. The war was not many weeks old before the Americans realized "those guys up there" were setting their depth charges too shallow, breaking off their ASW attacks too soon, and indulging in heady optimism concerning the results. Japanese airmen were not the only wishful thinkers. Imperial Navy men aboard destroyers, gunboats, sub-chasers and escort vessels frequently secured and sailed away in a glow of triumph entirely unjustified by the facts. A cheerful battle report always made good reading at Headquarters and enabled Tokyo Rose to broadcast an auspicious list of U.S. submarine obituaries. Many an embattled submarine owed its deliverance to Japanese presumption. And more than one submarine skipper could have quoted Mark Twain's, "The reports of my death are greatly exaggerated."

Although the Japanese antisubmarine effort was haphazard and, at times, almost lackadaisical, it managed to exact a punishing toll. Inferior though they were in many respects, the component ASW forces constituted a menace that meant trouble whenever encountered. The heavily armed destroyer, the ugly Chidori "pinger," the lethal mine and zooming plane, could be as deadly as lightning which strikes at random but kills when it hits.

While the Japanese did not have American sonar they did have their own echo-ranging system, and it was accurate to 3,000 meters. Additionally, the hydrophones were able to obtain a bearing at 5,000 meters. In 1942 the standard Japanese depth-charges were three hundred and fifty pounders (160 kilograms). These depth charges were built to explode at not over two hundred and fifty feet and they were not powerful enough to do great damage unless the attacking vessel achieved very nearly a direct hit.

Depsite its early inefficiency, as 1943 began the antisubmarine patrols of the Japanese Navy were becoming more effective. As the Americans were improving its air and surface search radars, the Japanese countered with devices that could detect radar emissions. In other words, the radar became a beam for the Japanese antisubmarine patrols. Progressively, as the Japanese patrols became more effective they were more aggressive.

Also, as 1943 began, the Japanese were developing radar. It was not yet installed on ships, but it was coming. They were adept, however, at the use of radio detection finders. The submarine that came to the surface and made a long transmission to Pearl Harbor might find that it had raised a nest of hornets. The Japanese had another device not duplicated in the United States, the jikitanchiki, a magnetic detector used by Japanese aircraft. It sensed the presence of a large metal object below the surface of the sea, so that low-flying pilots could sometimes find and track a sub that was submerged. However, at this stage of the war, the major Japanese ASW weapon was the sonar system. The Japanses sonar was technically superior and their employment of the echo-ranging techniques excellent. Also, as the war continued, more Japanese merchant ships were armed with deck guns that were a constant threat to any submarine trying to attack on the surface.

Most important at this stage of the war was the increase in Japanese production of antisubmarine vessels. The most effective of these were the kaibokans. These vessels were small, under 1,000 tons. At first the Americans thought they were only coastal frieghters, but they carried highly trained ASW crews and three hundred depth charges.

Still, the Japanese were so short of antisubmarine vessels that escorts were unavailable for most runs. The exception in the early months of 1943 was the shipping between the Dutch East Indies, Singapore, and Japan. Ships coming from that area brought rice, rubber, tin, and oil, all vital to the Japanese war effort. From the beginning, these convoys were protected by warships. Early in 1943, most other shipping had to depend almost entirely on locally supplied patrols and on air patrols. Supposedly, any alert would bring air protection to Japanese ships under attack, but in fact the air force protection didn't work very well. The Japanese had also begun to sow mines in the open waters, and as the war progressed these offered more danger to the submarines than the ASW devices.

In mid-1943, for the first time, sinkings by U.S. submarines went up to a rate of more than a million tons per year. The Japanese had counted on the sinking rate to come down as they won the war. The Imperial Japanese Navy began to concentrate more on antisubmarine warfare and asked its shipyards to produce more ASW vessels. But the Japanese production machine was already feeling the pinch of replacement. The Combined Fleet asked for carriers to replace the five lost in battle. Destroyers were needed to replace those lost in the continuing South Pacific battles. Admiral Yamamoto was dead, but his dire prediction was becoming fact: skill, courage, and determination notwithstanding, the Japanese were starting to fail beneath the heavy weight of American war production.

Still, in the month of September, the first of the new antisubmarine vessels were being delivered. Brash souls in high places were comforting themselves with the knowledge that the American submarine torpedoes were faulty and often did not explode — just at the time when the torpedo problems were being fixed and the rate of sinkings was about to jump.

In the closing weeks of 1943, Japanese ASW efforts were growing more effective. The IJN did have one superior weapon: the remarkably efficient radio-detection system. Admiral Lockwood, Commander Submarines Pacific, was quite rightly concerned about the enemy ability to locate a submarine by its radio transmissions.

As 1944 began, Japan employed the first of its new hunter-killer teams of ASW vessels. A convoy taking troops to the Marianas was attacked by the submarine Trout. The sub sank one transport and damaged another. Then three Japanese destroyers began a combined attack on the Trout and sank her. The experience was an indication of the changing nature of the submarine war in the Pacific: the American submarines were growing more aggressive and skilled in their task, but so were the Japanese ASW vessels.

In the meantime, Admiral King responded to the increased Japanese antisubmarine patrol and escort services with a new directive to the submarine fleet to concentrate on destroyers and escort craft rather than carriers and battleships. It was a reflection of the success of the Japanese efforts.

A real struggle was developing between the submarines and the escorts in the middle of 1944, one that transcended the usual. The Japanese were constantly devoting more resources to antisubmarine warfare. The number and size of the Japanese minefields were increasing, and the IJN was learning more about the American submarines. One source of information, unsuspected by the Americans, was the talk-between-ships carried on by the wolfpacks and by sub skippers who happened to encounter a friendly boat at sea. The Japanese antisubmarine command scoured their universities and business firms and put together and intelligence team of experts in American vernacular speech; they also secured a good deal of information about submarine operations by monitoring voice broadcasts.

In mid-1944, the American campaign against Japanese merchant shipping emerged as a major factor in slowing the ability ot the Imperial forces to prosecute the war. So many ships were sunk in the East China Sea and the waters of the East Indies that war production was affected. To meet the threat the Japanese were constantly improving their ASW methods. One major change was the gathering of the Grand Escort Force under the direct control of the Combinded Fleet. Much of the strength of the escort force was located at the southern Formosa port of Takao, which gave access to the Formosa and Luzon straits, the two greatest danger spots.

The Japanese used their aircraft to sweep an area thirty miles ahead of a convoy. If enemy submarines were encountered the planes sent word to the escorts or to one of the four auxiliary carriers assigned to the force. They made many attacks on U.S. subs in the next few months and operated under the misapprehension that they were sinking submarines at a rate of several each month — but actually they were not. In fact, the increased number of American submarines in the area continued to score often in spite of the Japanese vigilance.

The loss of the Harder, which had sunk a good many Japanese destroyers, gives a glimpse of the growing effectiveness of the enemy's ASW efforts. On August 24, the Hake saw two ships emerge from Dasol Bay. These ships were a kaibokan and the other the former American four-stack destroyer Stewart, which had been captured after it was damaged and put into drydock in Java. The Japanese had rebuilt the Stewart and renamed her Patrol Boat No. 102.

The Hake went deep to evade. The two patrol vessels, joind by an airplane, were on their way to search for the submarine that had sunk the destroyer Asakaze earlier that day. The plane diverted the Harder by dropping a depth bomb, forcing the sub to dive. Then Patrol Boat No. 102 moved in. The old destroyer had been turned into an effective antisubmarine vessel. She had 72 depth charges: 220-pound charges effective to a radius of 150 feet. She began dropping them in patterns of six charges as she ran across the spot where sonar reported that the Harder was lurking. The first set of charges exploded at 150 feet, the second at 180, the third at 270, the fourth at 360, and the fifth at 450. After the fifth run, oil began coming to the surface, followed by wood splinters and large pieces of cork. The old destroyer stayed in the area and made a sounding. It seemed that the sub had sunk in 900 feet of water. As they remained in the area other bits of debris came to the surface and the crew knew that they had killed the sub for sure.

But time was against the Japanese as American forces began to close the ring around Home Islands. The vigorous struggle between the subs and the escorts would continue, even as the squeeze on Japan tightened. So desperate was the Japanese need for oil that they began sending many escorts with single tankers from the oil fields all the way to Tokyo Bay. On October 30, south of Kyushu, the Trigger torpedoed a ten-thousand ton tanker; it didn't sink. Later that day the Salmon caught up with the same tanker and attacked — even though it was protected by four kaibokans. The sub sank the tanker and was then attacked by the escort vessels. They damaged her so severely that she had to surface to avoid sinking. The Salmon spotted a single escort and charged in with guns blazing, and then ducked into a convenient rain squall and escaped. The sub made it back to base in the Marianas, but she was damaged so badly that she never went out on another war patrol.

As 1945 began, more U.S. submarines were at sea, but they were sinking fewer ships, and the vessels they did attack were much smaller. The campaign against the Japanese marine had been so effective that the Americans were running out of targets. Lucky was the skipper who found a two- or three-thousand-ton frieghter in his path. Most of them were already on the bottom.

But the Americans were also becoming aware of an enormous improvement in Japanese ASW techniques. An improved radar was the answer, in systems used by planes and escort ships. As deadly as this improvement was, it was too little, too late for the Empire of Japan.


[Sources: Pig Boats: The True Story of the Fighting Submariners of World War II by Theodore Roscoe (US. Naval Institute: Annapolis, MD, 1949) and Submarines At War by Edwin P. Hoyt (Stein and Day: New York, 1983).]
Thanks to member DanielMcintyre. :up: