[TEC] Depth Charge values examined in S3D

[I-25]

Originally Posted by mrbeast

I read about the happening somewhere can't remember where though, the crew could hear the DCs rolling down the side of the conning tower! I also recall an instance where a sub or U boat surfaced and had a dud DC caught on the deck casing! How about opening the hatch and seeing that little baby sitting there?!

This happened to the I-176 North of Rabaul in 1943 after dropping off supples and evacuating wounded solders from finchaven. The XO said that one night a B-25 suddenly came out of the sky and they crashed dive under a hail of 50 cal. fire at about 20M down they heard a thump and a small boom like a firecracker. they came back up after a few hours and as they opened the hatch in the tower the first guy out must of freaked out. the charge was laying inside the tower bridge. they say some sort of yellowish substance was around it. the detonator had gone off but it didn't set off the main charge. Lucky Lucky japs!. On that same mission while at finchaven they got bombed by more B-25's while in the bay at night, the Capitan got shot (not mortally). and the XO beached the sub on a reef. after plugging up all the holes over night they waited for high tide to get the sub back off, high tide came and the sub wouldn't budge. then came the order from the bridge "all hands on deck". from atop the tower the XO ordered with a megaphone "Ok now, everybody run from one side of the boat to the other" and by god knows how Japanese ingenuity worked and the boat started rocking and they got it off!

[tater]

I just read Japanese Destroyer Captain: Pearl Harbor, Guadalcanal, Midway - The Great Naval Battles As Seen Through Japanese Eyes.



Anyway, he mentions dropping charges (early in the war) set to 50m. Totally different than the only other info I had from navweaps.

Hmmm.

[DrBeast]

As expected, tater...there's always three sides to every story

[tater]

Good book, BTW.

[Ducimus]

I wonder if....

one took a hedge hog, gave it the DC rack model, and then if possible, fixed it so only 1 hedge hog (also being changed to use the DC barrel model) was launched per attack, and then used that as a substitue for the depth charge rack.

IF that would work, you could force it to explode at a set depth. I have my doubts, but its an idea worth a try.

[Nisgeis]

Originally Posted by tater

Good book, BTW.

I'm reading that one now.

In 'War in the boats' by Captain William J. Ruhe, there is the following passage:

Levelled off at 350 feet, the Crevalle then caught another string of depth charges. They exploded almost as close as the previous string of charges, but a little more above the hull. I noted that the explosions indicated that the Japanese were now using a one-hundred-meter-depth setting on the charges. The prior charges had exploded at close overhead as the Crevalle passed 170 feet, indicating that the first string were set at fifty meters. The Crevalle was thus operated at 400-foot-depth so as to straddle the charges with their 50, 100, and 150 meter depth settings.

He mentions the 150 meter depth settings a couple of times.

I've also read in at least one patrol report (can't remember which one, Pampanito?) estimates of depth charges exploding below them at about 425 feet.

[tater]

The later type 2 had more settings. The Type 95 was supposedly 30, 60, and later 90m.

Given that they were on the receiving end, any guesses as to the depth setting were guesses, though.

War in the Boats is great, too.

[Nisgeis]

Originally Posted by tater

The later type 2 had more settings. The Type 95 was supposedly 30, 60, and later 90m.

Hmmm, what source are you getting your info from? Would be inetersting to read it. I've spent a while doing some research on this and the following is what I have come up with and it seems to support your info and mine. The Type 95 setting for 90m seems to have been a stop gap measure, early on it only had 30m and 60m settings.

War Damage Report No. 58, which details damage sustained by submarines during World War Two, covers all types of damage sustained by submarines, including collision, gunfire, mine, torpedo etcetera. It's located here:

http://ibiblio.net/hyperwar/USN/rep/...8/WDR58-1.html

In that it references 'Handbook of Japanese Explosive Ordnance, OpNav 30-3M of 15 August 1945 and Bureau of Ordnance Pamphlet 1507 of 20 April 1945' and says the following:

3-10. The pistols for both the Type 95 and type 2 depth charges were also almost exact copies of early British models and both operated on the same depth setting and firing principle, although they were not interchangeable between the two types of charges.12 The firing mechanism of both pistols was actuated by the hydrostatic pressure of sea water flowing through a small orifice and slowly filling up an inner cylinder. Depth setting was accomplished by varying the size of the water inlet, thus determining the amount of time required to fill the inner cylinder. The smaller the inlet, the deeper the setting. The Type 95 depth charge pistol used early in the war could be set for operation only at depths of 98 feet, 98 feet with parachute, 197 feet, and "Safe". Later modification of this pistol provided for an additional setting of 292 feet. The maximum range of depth settings for the Type 2 depth charge pistol was much greater, a choice being available of 98 feet, 197 feet, 292 feet, 390 feet, 480 feet,and "Safe". It was apparently not possible with either type pistol to choose depth settings other than those enumerated above,even though detonation at some intermediate depth might be considered desirable.

3-11. No data are available as to how much variation could normally be expected between the prescribed depth settings on the pistols and the depths at which charge detonation would actually occur. The amount of error would naturally be affected by variations in sinking rates due to the following factors: (a) the method of launching, i.e., whether the charges were projected from throwers or dropped from stern racks; and (b) by the condition of the sea, i.e., whether still or disturbed. The accuracy with which the orifices in the pistols were initially machined would also affect the detonation depth. Tests conducted by the British on their early pistols indicated that discrepancies of as much as 60 feet should be expected for charges set for detonation at 250 foot depth. It should be noted that even though a Japanese depth charge were to come to rest in water more shallow than that for which its pistol had been set, it would still fire when sufficient water had seeped through the entry orifice to provide the minimum pressure required. This is believed to account for many of the delayed depth charge detonations which have been reported by U.S. submarines.

Although the Type 2 charge could be set to 480 feet, it seems that the maximum setting normally used was 390 feet. This is also corroborated by the 'REPORTS OF THE U. S. NAVAL TECHNICAL MISSION TO JAPAN', which can be found here:

http://www.fischer-tropsch.org/prima...USNTMJ_toc.htm

The report entitled 'Japanese Anti-Submarine Warefare' slightly contradicts the above report and says that a depth charge pattern for both coastal defence and destroyers contained a mix of depth settings of 30m, 60m, 90 and 120m. It says:

'The Japanese had no means of determining the depth of enemy submarines, and their depth charge patterns were designed to cover all depths within the limitations of the depth settings on their charges.'

The contradictory part is:

Maximum depth setting of charges usually carried was 120 meters and a proportionate number of charges with this setting was included in each pattern.

That disagrees with the maximum depth setting of 480 feet on the Type 2, but it cannot be a Type 95 as that only went to 90m. It then goes on to say:

"Q" deep-setting pistol for depth charges had been developed, but, apparently, issue to ships had not become general and no specific doctrine for its use had been developed. Inasmuch (sic) as deep-setting pistols had been designed it is possible that the Japanese were working on the idea of special procedure for this type of attack.

I cannot find any other reference to a "Q" pistol, but there is a refence in the report 'Japanese Depth Charges', to a Type 3. 'Japanese Depth Charges' opening states:

'The purpose of this report is to provide information about the Japanese depth charges, namely influence and standard depth charge pistols. Interrogation has revealed that onlt two influence depth charges were under consideration, and of these, only one was approaching finality of design. Drawings supplied by the Japanese of depth charge pistols are included.'

The report describes the two influence depth charges as magnetic influence (Type 4, part tested but never used operationally) and Accoustic Depth Charge (no designation, presumably as none had been built). The magnetic influence depth charge was set to detonate when in proximity or if nothing triggered it, it was set to explode at 656 feet (200m).

It then details the type 3 model 1 pistol, which is similar to the type 2 pistol, but extra time required for reaching the greater depth is provided by a delay train which is initiated by the firing pin (hydrostatic). Depth settings for the Type 3 Model 2 depth charges are at 131.2 feet (40m), 262.4 feet (80m), 393.6 feet (120m), 524.8 feet (160m) and 656 feet (200m). It doesn't say specifically, but it doesn't look as though the type 3 pistol would fit in the type 2 depth charge, so I don't think it would be retrofitted. Perhaps this type 3 is the afforementioned "Q" type?

Given that they were on the receiving end, any guesses as to the depth setting were guesses, though.

Well, that is certainly true for far depth charges, but for close and very close depth charges, where you get a shock wave, I think you'd be able to tell which direction it came from. Certainly close depth charges would move the boat and it was established that depth charges close underneath your boat would also cause you to rise and likewise depth charges close above would force you down. I don't think they had a problem knowing where the depth charges were exploding, not that it helped them. The DCDI was developed primarily so captains could get an understanding of where depth charges were exploding when they were not close, so they could determine where the Japanese thought they were and maneuver accordingly. There are however two accounts mentioned, in WDR 58, the first of the USS Seahorse 4th July 1944, during the fifth patrol of of depth charges being dropped and at a depth of 470 feet, the DCDI indicated that the depth charges were exploding below her. USS Threadfin reported that whilst being depth charged on 28 March 1945, during her second patrol, over half the detonations occurred at depths greater than 450 feet as indicated by the DCDI.

War in the Boats is great, too.

It certainly is. Unfortunately for me, most of the submarine books are only available in the U.S. and not where I am .

Anyway, hope this helps the discussion of depth charges, there is also discussion of air dropped depth charges in WDR 58.

Edit: Stocks of Type 95s seem to have been used up by mid 1943, their use overlapping the Type 2s