WesWorld

Testing of torpedoes.

Greece and Turkey are at war. A Greek convoy is pushing through to Smirnya at night. Through spies, the Turks have assertained the convoy destination and estimated arrival. Three torpedo boats are sent to intercept the convoy.

Just before midnight the forward sentry for the convoy, the Greek Gunboat Elektra is traveling east at 15 knots and spots unknown vessels to the South East. She flashes a challenge to the mysterious vessels 5000 yards away and the reply is in a hail of gunfire with the Elektra taking 2 4" hits as the Turkish ships alter course and accelerate. The lead TB launches three torpedoes at the gunboat. The torpedoes are typical 1920's era with a speed of 36 knots, a range of 7000 yards and a 515lb warhead. The two 4" hits do some damage to the stern with a loss of 1 knot of speed.



As it is night I'm doubling the range to calculate hits. I'm also allowing for higher rates of fire from QF guns by doubling the number of guns firing. I think I should have a gunnery modifier but I'll have to calculate one. Using a searchlight pinpoints yourself and has an effective range of 8000 yards. Firing your guns also pinpoints yourself. Proceeding at more than 20knots gives a visible bow wake at night.



The Turkish torpedo boats are 32knot vessels of 600 tons with 2 4" guns and 6 21" torpedo tubes. They can take 411 points of damage each.

The Greek Gunboat is 1874 tons with 7 5" guns (3 forward, 4 aft) and a speed of 24 knots. She can take 3291 points of damage. In gunfire alone, the gunboat can absorb 100 4" 32 pound shots but about 20 would mission kill it. In contrast, the fragile torpedo boats can take only 6-7 5" hits before sinking.

With the action opening at 00:03, the Elektra accelerates to 20 knots and opens fire on the lead TB at 00:06 where the range has dropped to 4500 yards. The lead Turkish ship is hit by 4 5" shells, one penetrates a boiler, one the bow and the last two are non-critical. She has been heavily hit with speed reduced to 10 knots. Before pulling out of line she fires her remaining 3 torpedoes while the second TB also empties a bank of TT. The TB also hit Elektra twice more but neither shell does any critical damage. Note that the torpedoes fired at 00:03 have not reached the gunboat.



With the TB slipping past Elektra to the south, the gunboat turns 180 degrees. In doing so she has entered the zone for the 00:03 torpedo spread. The forward edge of the torpedoes are in blue box and are at a speed of 36 knots. As Elektra slows in the turn, there is a 4% chance of a hit but all three torpedoes are misses. Neither side hit with gunfire but the second TB, now leading, launches three more torpedoes. Both torpedo boats turn 45 degrees to starboard.



At 00:12 The 2nd TB is hit by 3 5" shells, one disables the engine and she too has to pull out of line and limp off to the south. The Elektra passes through the 00:06 launched spread of six torpedoes. All miss. None of the torpedo boats hit Elektra with gunfire. The original leader is pulling out of range to the south and is not firing to avoid drawing attention to herself.



At 00:15 the action is transformed. Elektra is hit by a 4" shell but that is the least of her problems. The three torpedoes launched at Elektra reach her and one slams into the boiler room losing 12 knots speed. To calculate damage I've used the size of the warhead multiplied by a percentage/12.5. For the 515lb warhead this gives a range of damage between 41.2 (a virtual dud) and 4120 (sink the gunboat in 1 hit). In this case the percentile or die roll was 32 so the torpedo will do 1318 points of damage. As this is a small warship the flooding would affect the whole compartment so I'm inclined to ignore the 889 points at which the ship would capsize but I'm open to suggestions. There needs to be a point where a torpedo would break a ships back. The Type 93 could chop a DD in half but it had a much larger warhead. Perhaps we could say if the damage is greater than 75% that the vessel can take then the ship is broken in two (2468 points in the gunboat case or a 40% chance of an instant kill). If the ship's beam is under 50 feet then we could say that the Capsize point is doubled (1778 points or a 57% chance that the ship will capsize from the hit). Springsharp rates the Gunboat design at 1.1 torpedoes.



With the cumulative damage, Elektra has been reduced to 2 knots speed. At 00:15, the undamaged TB is hit by 1 5" shell at 5720 yards that does no critical damage but reduces her to 27 knots. This ship continues on to the west in search of the convoy.



At 00:18 Elektra turns her attention to the 2nd TB that is limping off to the south but still in searchlight range (8000 yards). The gunboat and the TB hit each other but the 3 5" hits disbale the TB's engine and cause flooding. The cumulative damage exceeds the damage the vessel can take so she goes under at 00:21.



The engagement ends at this point with one TB heading west at 27 knots and a second heading south at 10 knots. Both are out of searchlight range. The Elektra is effectively dead in the water and would have to be towed or abandoned. The Turks expended 12 torpedoes for 1 hit and lost 1 ship with severe damage to a second. Without that torpedo hit they would have lost two ships and possibly all three with only light damage to the gunboat in return.

Does this seem 'realistic'?

Cheers,

Pretty good, actually. I'd consider having an actual dud roll for the torpedoes, and then a less broad range of damage for the fish rather than the range you have now.

Well yes torps usualy do lots of damege its not like a torp can hit not vital area everything under the water line is vital to the ship survival.
I second Hrolf on "less broad range of damage for the fish"

I dont know about duds depends on a period but for every 100 torp one is a dud seams resonable.

And what about sea state.Did you impimented it?

I'm not so sure on the damage factor. A 533mm torpedo hits the boiler room, i.e. the middle of ship and just causes the speed to reduce by 12knts? It sounds almost as hopeful as the interwar RN exercises where an R-class took 4 torpedoes and suffered only from a small speed reduction.

A quick look at other vessels of similar size that had torpedoes hit them. About 90% sank with the remainder suffering major damage.

I'm not sure about the 12:1 hit ratio. 6:1 might be more reasonable given the short range of the encounter.

I tried to look up the information about ELEKTRA but had to notice there is little to none in the Greek section of our encyclopedia... Looks like you have some work to do, alt_naval. :o) Would you please add the full SS files there? Many thanks...

To your question: I think one can expect such a gun boat to survive a TT hit - if surviving means it keeps floating. Unlikely probably but it could happen. Not that a 32 out of 100 is not a very high roll. I guess a 50+ would have sunk her?

What I do not agree to is that 102mm shells would do little damage to such a vessel. She has some minor armor but it wont keep 4" shells out of her vitals... However, as you said 20 hits may disable her which seems more realistic.

In general I think you´re not far off the mark with your calculations.

I agree, the damage calculation seems just a wee bit off but not by much. The torpedo accuracy does however seem spot on.

Hoo,

The Gunboat is here under 'Gunboat Springstyle'. They were lightened after the enclosed turrets were too heavy (See Gunboat )

I don't have the TB handy. I think I wrongly described the TT as banks of 3 and the drawing has 3 twins but it did have 6 21" torpedoes.

RA, the torpedo hit took out the boiler room (this design should have only one but my spreadsheet must assume 4 boiler rooms) This cut 12 knots but the torpedo damage of 1318 points took a further 10 knots so this renders the gunboat DIW with 1-2 knots of headway. The torpedo has crippled the ship but it did have the opportunity to kill it. HMS Kelly survived two hits IIRC.

You are right that most DD don't survive a torpedo hit and SS reflects this.

The torpedoes run 5-6 minutes before hitting. In Solomons fighting it was 1-2 minutes but the Type 93 was at 49 knots, not 36 in this case. I think 12:1 is fair in this case.

I need a way to reflect TDS as noted in SS. Possibly we use the 'torpedoes to sink' by 100 and the torpedo must exceed this number to do damage to the vitals.

Duds were more frequent than 1%. I'd be inclined to treat duds as misses. Maybe we could assume that a torpedo if it hits, is going boom and causeing at least equal to the warhead size or bigger.

I haven't worked on sea state yet.

Cheers,

Quoted

RA, the torpedo hit took out the boiler room (this design should have only one but my spreadsheet must assume 4 boiler rooms) This cut 12 knots but the torpedo damage of 1318 points took a further 10 knots so this renders the gunboat DIW with 1-2 knots of headway. The torpedo has crippled the ship but it did have the opportunity to kill it.

That makes more sense now.

The standard of torpedoes used in calculating the TDS rating in SS is a 20"/500mm torpedo. You seem to have already a way of changing warhead size however.

What doesn't make sense is after being gutted by a torpedo it still moves 2000 yards and still moving. I think it should be stopped by the end of the next turn.

Cheers,

Well, that´s physics for you, right? The ship has some weight, actually the torpedo adds to the weight, and with a given speed at time x it will continue its way while slowing (no force pushing it forward anymore after the hit).

So I would think somethings from when she would stop immediately....