Research Thread - IJN vs. Allied ASW

[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.

[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]

Originally Posted by 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?

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.

[quote]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.

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/prima...ort%20S-24.pdf

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

[panthercules]

Originally Posted by 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?

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.