A homing Type 93 Long-Lance torpedo

[Dilandu]

The major problem of the famous Type 93 "Long-Lance" torpedo was, that it wasn't exactly very effective in its intended role as long range weapon. The hit probability on extreme distances was just too low, and unless the target was unaware about the possibility of long-range attack, it was almost impossible to achieve a hit. The direction wander of Type 93 on max range was about 1500 meters, right or left, after all.

So my idea: let's give Type 93 some homing capability.

By reducing the oxygen supply tank (as it was done on late-war Type 93 Mod 3 torpedo) and fuel vessel, we could free about a meter of torpedo's lenght, while still having 30 km max range on 36-38 knots. The space therefore freed, we could use to install (behind the standard engine section) the electric motor and reduced battery from Type 92 electric torpedo. The electric motor is installed on the shaft of the torpedo propeller. The idea is, to give Type 93 "Long-Lance" the ability to run silently on electric for 2-3 km.

In the head section of Type 93 torpedo, we would install the pair of hydrophones, amplifying circuit and differential relay from the experimental Type 1 acoustic torpedo (based on Type 92, tested in 1943-1944). The control system would be linked with Type 93 gyro, thus allowing to guide the torpedo toward the source of engine noise (enemy ship).



The concept of operation: the modified Type 93 is launched from the standard torpedo tube at long distance. The torpedo made 30 km run on 36-38 knots, using oxygen-kerosen powerplant. At pre-determined momen, the timer would swithc off the piston engine, and power up the electric motor and acoustic homing system. At reduced speed, the "homing Long Lance" would be able to went 2-3 km silently enough for the homing system to actually guide it toward the enemy ship.

 

[JWilly]

1. Vessels, including torpedoes that are to steer require a degree of rudder authority inversely proportional to their length-to-beam ratio.

A WWII acoustical homing torpedo seeker had only a very short range before the acoustical signal was so attenuated and masked by ocean sounds and often other vessels' sounds, that no seeker lock was achievable. The torpedo needed a turn radius significantly less than that seeker lock range.

The Long Lance's case length would be a bad way to start a steerable-torpedo design. A relatively low-power electric motor would not be able to generate enough thrust to overcome the drag imposed by the extreme rudder-area to turn such a long case around such a relatively small turn radius. Much better to start from scratch.

2. Acoustical homing torpedoes in the pre-computer era were only effective against targets that were moving at a fraction of the torpedo's speed. The torpedo inherently steered toward the target's current position; assuming the torpedo was approaching from other than dead ahead, the target would continue to move so that eventually the torpedo was stern-chasing it. An electrically powered acoustical homing torpedo during WWII could only be fast enough, over a practical range, for use against very slow vessels that in addition were noisy enough for the acoustical seeker capabilities of the time, and were operating alone in relatively quiet areas of the ocean. (No nearby shoreline, numerically low sea state and wind condition, minimal fish/predator presence.)

Much better to combine the acoustical seeker capability with a more powerful propulsion system, if the intent was for the resulting weapon to be useful against vessels that might be moving at warship-cruise or warship-attack speeds. Then at least the power would be available to allow use of a greater-authority rudder.

 

[A Tentative Fleet Plan]

Would a passive acoustic seeker still work with the flow-noise of a much faster torpedo?

 

[TomS]

Would a passive acoustic seeker still work with the flow-noise of a much faster torpedo?

The Germans managed to get the G7es (T V) to work up to 24-25 knots--beyond that self-noise was too much. It topped out at about 5000 m range, which is probably a limitation on the seeker. If fired beyond that, it was unlikely to be close enough to the target to detect and track effectively. And it was limited as to the speed of target it could engage.

German U-Boat Torpedo T V (G7es) Acoustic Homing - Specification

The T V (G7es) was an acoustic homing torpedo which would home in on the target's noise signature. It was designed to be used against escort ships.

www.uboataces.com

G7es Type V Torpedo

G7es Type V Torpedo

ww2db.com

 

[Dilandu]

Would a passive acoustic seeker still work with the flow-noise of a much faster torpedo?

That's why I suggested to install auxilary electric drive on Type 93 - so the last leg of torpedo run could be done silently (albeit on reduced speed).

 

[GTX]

The major problem of the famous Type 93 "Long-Lance" torpedo was, that it wasn't exactly very effective in its intended role as long range weapon.

And yet it is still credited with 23 Allied warships sunk: 11 cruisers, 11 destroyers, and one fleet aircraft carrier.

 

[T. A. Gardner]

By what tentative date would this weapon become available?

 

[A Tentative Fleet Plan]

The Germans managed to get the G7es (T V) to work up to 24-25 knots--beyond that self-noise was too much. It toped out at about 5000 m range, which is probably a limitation on the seeker. If fired beyond that, it was unlikely to be close enough to the target to detect and track effectively. And it was limited as to the speed of target it could engage.

German U-Boat Torpedo T V (G7es) Acoustic Homing - Specification

The T V (G7es) was an acoustic homing torpedo which would home in on the target's noise signature. It was designed to be used against escort ships.

www.uboataces.com

G7es Type V Torpedo

G7es Type V Torpedo

ww2db.com

That's why I suggested to install auxilary electric drive on Type 93 - so the last leg of torpedo run could be done silently (albeit on reduced speed).

That pretty much confirms my suspicions.

What about pattern-running?

British torpedoes were tested with this capability during the First World War, and it entered service during the Interwar period aboard British Destroyers as "W Gear", intended for pretty much the same purpose as the Type 93, (i.e. long-range Browning shots against an enemy battlefleet, with the pattern-running being intended to provide a higher hit-rate against lines of enemy battleships).

Could the Anglo-Japanese Naval Cooperation have led to this knowledge becoming available to the Japanese prior to 1921, or alternatively could the Japanese have stumbled across it at a later date, in much the way that British work on Oxygen Torpedoes that led to the 21" Mk VII and 24.5" Mk I inspired the Type 93?

 

[JWilly]

The major problem of the famous Type 93 "Long-Lance" torpedo was, that it wasn't exactly very effective in its intended role as long range weapon.

And yet it is still credited with 23 Allied warships sunk: 11 cruisers, 11 destroyers, and one fleet aircraft carrier.

None of those kills were at a range anything like the weapon's maximum, though.

 

[JWilly]

A better direction than acoustical homing for the Long Lance...since acoustical homing technology wasn't mature enough for use against cruise-speed or attack-speed warships during WWII...would have been to develop an even faster moderate-range version for conventional aimed-fixed-course use.

 

[SSgtC]

That's why I suggested to install auxilary electric drive on Type 93 - so the last leg of torpedo run could be done silently (albeit on reduced speed).

Except the electric motor would probably only give the torpedo a max speed of 20-25 knots (at least without blanking the hydrophones with flow noise). Considering the US/UK warships that the weapon would be fired against at long range would all likely be doing at least 25 knots, that pretty much means the Long Lance goes from a very low hit probability to zero hit probability. Just from the simple fact that the torpedo can't catch them unless it's a down the throat shot.

 

[JWilly]

The Long Lance would have been the wrong candidate for such a development. There would have been no way for a torpedo as long as the Long Lance to have enough rudder authority, with a rudder no higher than the torpedo diameter so as to not require re-designed launchers and handling equpment, to be very maneuverable...and since WWII acoustical homing did not work at long ranges, why bother with a torpedo that would have been unlikely to be able to turn sharply enough to home on targets that required significant steering to hit?

A shorter-ranged, very maneuverable torpedo, on the other hand, could have been useful.

Japanese submarines, if their doctrine had focused on sinking freighters instead of warships, would have been likely to be opposed by relatively slow convoy escorts--DEs, corvettes and the like--that for much of the war had to manuever close to the sub's position to attack it. An ability for a sub to fire a short-range, fixed-three-meter-depth homing torpedo that would counter-attack such attacking escorts would have been a great survival tool.

WWII electric torpedoes were not fast enough to catch most warships in a stern chase, and the necessary computer technology did not exist yet for homing torpedoes to calculate and steer an intercept course; but such torpedoes were fast enough to catch such convoy escorts.

Apparently Japan experimented with acoustical homing versions of their Type 92 electric torpedo http://www.navweaps.com/Weapons/WTJAP_WWII.php, as mentioned above by Dilandu, but at 28 knots the torpedo itself generated too much noise for the acoustical homing to work.

 

[Foo Fighter]

Was there a capability to dash and then reduce speed in the terminal phase?

 

[SSgtC]

Was there a capability to dash and then reduce speed in the terminal phase?

Unless you're targeting a slow merchant, slowing to aquire the target means you can't catch the target.

 

[Grey Havoc]

Perhaps use the Long Lance as a 'bus' to deliver a smaller homing torpedo to the vicinity of a high value target, without alerting the target or any escorts until it is too late?

 

[JWilly]

Perhaps use the Long Lance as a 'bus' to deliver a smaller homing torpedo to the vicinity of a high value target, without alerting the target or any escorts until it is too late?

How would that system be launched?

Maybe existing launchers could be used if the electric homing torpedo fit inside a re-designed Long Lance body...but the body length could not be increased, if use of existing launchers was desired.

The warhead volume of the original Long Lance body was not long enough for an electric torpedo with large enough batteries and warhead of its own. Plus, some volume would have to be devoted to the mechanism for determining when the Long Lance had reached the ejection point and should stop/open/launch the electric homer. It's not clear to me how that would work.

Plus as noted this weapon would only be useful against moving (thus sound-generating) targets that were no faster than maybe 16 knots, so the electric homing torpedo could catch the target in a stern chase.

Seems like it would have been a complex development project with WWII technology and capabilities.