Japanese 720mm torpedo

[YourChair]

Hello,
Does anyone have information on the Japanese 720mm torpedo? Several people (some Japanese and Chinese blogs and some guy on Axis history forums) have mentioned a 720mm torpedo developed from 1944 into 1945. However, the response to that post: https://forum.axishistory.com/viewtopic.php?t=161549
cites Lacroix's Japanese Cruisers of the Pacific War (as a tangent, I would love to have that book, but the price tag is crazy, $160 minimum). Apparently a 720mm Type 0 torpedo existed, which fits the bill for the various characteristics and descriptions ascribed to the supposed 1944 torpedo:

Projected characteristics:

• Diameter 72cm
  Length 11.5m
  Weight 5000kg
  Warhead, 850kg Type 97 explosive (60% TNT and 40% hexanitrodiphenylamine)
  Oxygen pressure 250kg/cm2
  Range 27,000m at 55 knots; 30,000m at 50 knots; 54.000m at 40 knots.

Can anyone confirm some of this information?

 

[Tzoli]

The data table from said book:

And the only small text mentioning it:

 

[airman]

I suppose 720 mm torpedo was only a project .

 

[Colonial-Marine]

A destroyer would be getting to the size of a light cruiser just to carry a decent number of those.

 

[WatcherZero]

Would have been the largest conventional torpedo if it had entered service.
There was the British 24.5 inch (622mm) torpedoes only carried by the Nelson class battleships and the Soviet 650mm torpedoes that entered service on their subs in the 70's to incorporate a nuclear warhead, but most of them were reduced to 533mm tubes via inserts. Seawolf class got 660mm tubes as they assumed a large calibre torpedo would be developed by the US Navy to match the Soviets but it never was.

 

[Bruno Anthony]

Would have been the largest conventional torpedo if it had entered service.
There was the British 24.5 inch (622mm) torpedoes only carried by the Nelson class battleships and the Soviet 650mm torpedoes that entered service on their subs in the 70's to incorporate a nuclear warhead, but most of them were reduced to 533mm tubes via inserts. Seawolf class got 660mm tubes as they assumed a large calibre torpedo would be developed by the US Navy to match the Soviets but it never was.

The USN didn’t develop a larger torpedo because there has been a lack of guts in several US weapons systems for some time.

 

[Bruno Anthony]

Hello,
Does anyone have information on the Japanese 720mm torpedo? Several people (some Japanese and Chinese blogs and some guy on Axis history forums) have mentioned a 720mm torpedo developed from 1944 into 1945. However, the response to that post: https://forum.axishistory.com/viewtopic.php?t=161549
cites Lacroix's Japanese Cruisers of the Pacific War (as a tangent, I would love to have that book, but the price tag is crazy, $160 minimum). Apparently a 720mm Type 0 torpedo existed, which fits the bill for the various characteristics and descriptions ascribed to the supposed 1944 torpedo:


Can anyone confirm some of this information?

All forum members will receive free copies of that book starting in January

 

[Bruno Anthony]

All forum members will receive free copies of that book starting in January

All forum members will receive free copies of that book starting in January

Teasing of course, they cost $hundreds per copy

 

[Dorknought]

Would have been the largest conventional torpedo if it had entered service.
There was the British 24.5 inch (622mm) torpedoes only carried by the Nelson class battleships and the Soviet 650mm torpedoes that entered service on their subs in the 70's to incorporate a nuclear warhead, but most of them were reduced to 533mm tubes via inserts. Seawolf class got 660mm tubes as they assumed a large calibre torpedo would be developed by the US Navy to match the Soviets but it never was.

The Germans had the H8 60cm 23.7" in their last WW1 BB and BC and on some CL and the large DD. They were also developing the J9 70cm 27.6" torpedo that was designed in 1912 presumably for follow on Baden class ships.

Pre-World War II Torpedoes of Germany - NavWeaps

www.navweaps.com

 

[A Tentative Fleet Plan]

Would have been the largest conventional torpedo if it had entered service.
There was the British 24.5 inch (622mm) torpedoes only carried by the Nelson class battleships and the Soviet 650mm torpedoes that entered service on their subs in the 70's to incorporate a nuclear warhead, but most of them were reduced to 533mm tubes via inserts. Seawolf class got 660mm tubes as they assumed a large calibre torpedo would be developed by the US Navy to match the Soviets but it never was.

Imperial Germany had the 60cm H8 Torpedo in service during the First World War, plus the experimental 70cm J9 Torpedo.

 

[WatcherZero]

As already mentioned J9 never entered service and H8 seems to be mostly a case of fitted for but not with, torpedo production was cancelled at the start of the war and despite a lot of ships having the tubes for them only a handful of ships ever received ammunition with no reported case of any ever being used in combat during WW1 or even test fired, smaller torpedoes were used instead and the submerged tubes were removed in 1917 because it was found to be a main structural weakness of the ships.

 

[Avimimus]

The thing I can't understand - those range figures! Why would someone need such a long ranged torpedo? I can see warhead size and speed, but the probability of a hit at 5km is already so low... if it isn't a manned torpedo I can't see the point in carrying that much fuel.

 

[Scott Kenny]

The thing I can't understand - those range figures! Why would someone need such a long ranged torpedo? I can see warhead size and speed, but the probability of a hit at 5km is already so low... if it isn't a manned torpedo I can't see the point in carrying that much fuel.

For unguided torpedoes, your target changes from "that ship" to "that fleet" or "that convoy" at those ranges. And the Japanese did get hits on US ships at extended ranges with the Long Lances, the US tended to attribute the explosions to mines instead of torpedoes.

 

[WatcherZero]

If you have a channel that might only be 10 miles across that the fleet has to pass through you have a perfect chokepoint to saturate and formations and convoys may be a dozen miles long.

 

[donnyjie]

From 《昭和造船史》, notice the third row from the last:




(g) The prototypes of the Type 0 torpedo: A large-scale oxygen torpedo with much higher performance than the Type 93. Its specifications are shown in Table 39. Its structure resembled the Type 93 but had a 4-cylinder vertical engine. The development was halted at the time when production just started due to the change of the war situation.

 

[Dilandu]

and the Soviet 650mm torpedoes that entered service on their subs in the 70's to incorporate a nuclear warhead, but most of them were reduced to 533mm tubes via inserts.

USSR actually have used a combination of 65-cm and 53-cm tubes. And it was not to fit a nuclear warhead - the first Soviet nuclear torpedo was in 53-cm size - but mainly to obtain standoff range with enough speed to reliably hit the carrier battlegroup order.

 

[Dilandu]

For unguided torpedoes, your target changes from "that ship" to "that fleet" or "that convoy" at those ranges. And the Japanese did get hits on US ships at extended ranges with the Long Lances, the US tended to attribute the explosions to mines instead of torpedoes.

They did, but the actual hit probability was much lower than Japanese anticipate pre-war. The absolute majority of Long Lance hits were obtained on standard torpedo distances.

The thing I can't understand - those range figures! Why would someone need such a long ranged torpedo? I can see warhead size and speed, but the probability of a hit at 5km is already so low... if it isn't a manned torpedo I can't see the point in carrying that much fuel.

Well, as far as I could understood, the general idea behind the 72-cm torpedo was to get more speed, not range. Apparently Japanese realized, that 61-cm torpedo took too long to go for the max range at 36 knot speed (and therefore have little chance to actually hit anything), so they decided to design bigger torpedo that could carry more fuel and thus run on higher speed (up to 50 knots)

 

[Scott Kenny]

They did, but the actual hit probability was much lower than Japanese anticipate pre-war. The absolute majority of Long Lance hits were obtained on standard torpedo distances.

yes, slow torpedoes make for a very complex and low probability engagement.

It's why all modern combustion torpedoes run at least 45 knots and Spearfish does 80. IMO electric powered torpedoes are only useful against merchant ships.

 

[Dilandu]

yes, slow torpedoes make for a very complex and low probability engagement.

It's why all modern combustion torpedoes run at least 45 knots and Spearfish does 80. IMO electric powered torpedoes are only useful against merchant ships.

Yep. Accroding to the table, the 72-cm torpedo was supposed to run 32.000 meters at 50 knots. The standard Type 93 (early model) was capable of running 30.000 meters at 40 knots. So on same distance, the 72-cm would be approximately 25% faster, thus reducing running time and increasing chances to hit.

P.S. Frankly, I suspect the chances to hit would still be abysmal - and Japanese Navy would get more results if invested in acoustic homing for long-range torpedoes. IRL, Japanese started to tinker with homing torpedoes (for both anti-ship and anti-submarine purposes) far too late to make any difference.

 

[Scott Kenny]

Yep. Accroding to the table, the 72-cm torpedo was supposed to run 32.000 meters at 50 knots. The standard Type 93 (early model) was capable of running 30.000 meters at 40 knots. So on same distance, the 72-cm would be approximately 25% faster, thus reducing running time and increasing chances to hit.

That is an immense improvement in terms of predicting where the target will be in 20 minutes versus 25 minutes.

P.S. Frankly, I suspect the chances to hit would still be abysmal - and Japanese Navy would get more results if invested in acoustic homing for long-range torpedoes. IRL, Japanese started to tinker with homing torpedoes (for both anti-ship and anti-submarine purposes) far too late to make any difference.

Yes, predicting where the target will be in 20 minutes is ... challenging, to say the least. It's why the best targets for unguided torpedoes at long range are fleets or convoys.

WW2 acoustic guided torpedoes seem to have a range of about 4000yards, so you'd still need a firing solution good enough to get your torpedo within about 4000yards and with the nose pointed within a pretty narrow arc (maybe 30deg wide, 15deg on either side of course?) to detect the target... And you'd want a magnetic influence sensor to have the guided torpedo break keels instead of just blowing a hole in the side of the hull.

Edit: NOSE, not noise... fumbletyping strikes again...

 

[Dilandu]

WW2 acoustic guided torpedoes seem to have a range of about 4000yards, so you'd still need a firing solution good enough to get your torpedo within about 4000yards and with the noise pointed within a pretty narrow arc (maybe 30deg wide, 15deg on either side of course?) to detect the target... And you'd want a magnetic influence sensor to have the guided torpedo break keels instead of just blowing a hole in the side of the hull.

If I recall correctly, Japanese experimented with sort of acoustic beam-rider - torpedo moving in narrow beam (more likely intersection of two beams) of sonar. Not sure it would be workable on long distances, thought.