John P. Cromwell attack technique on order

[WH4K]

Here's a weird thing I noticed: Before mid-1943, I got duds fairly often with the Mk. 14 (and derivatives), despite using the 45° impact angle and low-speed setting. I would even get duds when using a very low impact angle, such as nearly straight-on bow or stern shots on ships at anchor.

Or is that normal? Is it supposed to still be a crapshoot, even with an impact angle nowhere near 90°?

I didn't have much luck with the magnetic exploder either. Perhaps as many as 50% of torps fired with the magnetic exploder active would detonate well before reaching the target, which I gather is more or less what happened in reality.

It's now late 1943, and the magnetic exploder seems to work perfectly. As long as I set it a foot or so under the ship's draft, BOOM, it goes off as expected.

I thought the magnetic exploders never really worked correctly, which was why Admiral Lockwood ordered their use halted? I am profiting from disobeying this order.

[Rockin Robbins]

Shhhhhhhhhhhhhh! That admiral is reputed to sometimes frequent this forum!

[Giesemaschine]

Okay gents, I'm still trying to wrap my mind around this method (I haven't had too much luck) - I am also a complete NOOB to manual targeting and fleet boats in general, so bear with me.

Because this is a method using ratios, as long as I compute the correct ratio between degrees/distance (3600 yards or 46100 yards depending upon which torp. speed I use), the actual range from the target does NOT matter so long as I am:

1. Pointing exactly 45 to the target's course
2. Have my crosshairs on the lead angle (calculated by ratio above) and fire when juicy parts of ship pass by.

I'd prefer NOT to use the TDC, so with that being said, I am having some problems with a scenario I created to practice on:

Target ran 800 yards in 3 minutes, so he is doing 8 knots (correct?). At a 45 angle from 3600 yards to intersection, I measured the angle to his initial run and that is 8 degrees. So that means my lead angle (where I have to point the periscope) is at 352. Am I correct so far?

I've zeroed the AOB and Speed in the TDC, but what should I put for range? I can't zero out range in the TDC (lowest is 200) and it seems that the ranges I send to the TDC are effecting my torpedo runs, even though they shouldn't be?

I'm also placing my crosshairs dead-center on 352, but what happens is - I wait until the desired area I want to hit passes the crosshairs (let's say just under the bridge) - I fire a torpedo as the bridge passes by, but it's actually hitting way aft of the bridge, or sometimes missing altogether.

Help me out here

[ColonelSandersLite]

Originally Posted by Giesemaschine

1. Pointing exactly 45 to the target's course

I don't have time for the rest atm, but the above has nothing to do with it. What matters is a 0 gyro torpedo run. When both a target and a projectile have a constant course and speed, the lead angle does not change with distance. I know it seems counter intuitive, but it's 100% true. 45 degrees is just a part of his setup technique.

[Rockin Robbins]

That is exactly right. The reason range cancels out of the solution is that you are shooting a "straight shot" as defined by the US Navy, that is a shot with less than a 20% gyro angle. The smaller the gyro angle, the less range matters until you get to zero where range has no bearing at all on the accuracy of your shot.

Since I'm using rules of thumb and not calculations to picking a firing bearing the gyro angle is not going to be zero. It will be a small one digit number though and you will definitely hit your target.

Keep in mind that in the stock game where ships basically have no inertia, shooting a DD from ahead will usually mean that they dance out of the say of the torpedo and come after you. I'd avoid that.

But against merchies where you haven't been sighted and with ranges not exceeding 1200 yards it is pretty deadly. And if you miss you can set up for a 90º Dick O'Kane shot really quickly to snag him on the rebound.

I've found that the Cromwell attack has more of a chance of the torpedo being spotted and the ship maneuvering out of the way than a Dick O'Kane attack. It's a lot of fun with electric torpedoes. It's absolutely deadly at night.

You can modify the John P Cromwell attack to attack from any angle you wish. For instance on an attack from 50º in front, choose a shoot bearing 10º before your zero bearing, angle on the bow would be your approach angle (50º) minus your lead angle (10º in this example), so his angle on the bow would be 40º, either port or starboard depending on which side of the target you can see.

As soon as the part of the target you want to hit crosses your shoot bearing pull the trigger and that's where you will hit regardless of his range.

[SOFLCS]

Each method, be it the Cromwell, O'Kane, Sonar only, Radar only, night surface, are all tools, some specialized, some fairly broad. But in your toolbox everything flows through the TDC, it is your uniquely American advantage and incredibly versatile, as long as you give it range, aob, and speed it can track targets and let you shot anywhere your torpedoes can reach. Learn to use it by itself, not tied to any particular technique, learn about it's nuances, how to enter data, and you will have gained an amazing advantage.
Yes, 800y in 3 minutes is 8 knots. Range is not a factor when AOB and speed are zeroed, think of how the TDC works: you feed in data about an object moving in two dimensions and once it has an initial distance from you, range, the direction it's moving, aob, and how fast it's going it compiles data on where the ship will be as time passes. Now with speed zeroed AOB doesn't matter, the target isn't moving so the TDC doesn't adjust for anything. So no, it shouldn't matter. Range only applies when it's moving, and the TDC thinks the target is stationary. If the TDC thinks the target is standing still it won't calculate the collision course for the torpedoes, it will just keep it on the heading you selected through your scope/TDC.

[Rockin Robbins]

Originally Posted by Giesemaschine

1. Pointing exactly 45 to the target's course
2. Have my crosshairs on the lead angle (calculated by ratio above) and fire when juicy parts of ship pass by.

Great so far. You're right on the money

Originally Posted by Giesemaschine

I'd prefer NOT to use the TDC, so with that being said, I am having some problems with a scenario I created to practice on:

That's where you run astray. We DO use the TDC in our constant bearing attacks. What we don't use is the position keeper and the stadimeter. You still must enter the AOB and target speed into the TDC because it actually calculates the Torpedo Track Angle, the bearing the torpedo takes when it travels to the target. It will not be exactly zero. It will be a very small single digit number that renders range inconsequential.

Originally Posted by Giesemaschine

Target ran 800 yards in 3 minutes, so he is doing 8 knots (correct?). At a 45 angle from 3600 yards to intersection, I measured the angle to his initial run and that is 8 degrees. So that means my lead angle (where I have to point the periscope) is at 352. Am I correct so far?

I've zeroed the AOB and Speed in the TDC, but what should I put for range? I can't zero out range in the TDC (lowest is 200) and it seems that the ranges I send to the TDC are effecting my torpedo runs, even though they shouldn't be?

Help me out here

And that's your problem. You should have entered 8 knots into the TDC and pressed the send button twice.

Then you should have entered the AOB (45 minus your lead angle of 8º=37º) starboard if you're looking at the starboard side of the target or port if you're looking at its port side. Press the send button twice.

Then you have to have some non-zero range in the TDC because it goes stark raving crazy with a zero value for some reason. My video shows pulling down the range triangle to yield a range of 1300 yards or so in the TDC. Point your periscope down the shoot bearing and hold it there. Press the send button twice.

NOW you're ready to shoot as the juicy parts of the target pass the shoot bearing in your periscope. NOW you'll hit where you intended.

In this method your shoot bearing is somewhat arbitrary, being picked by rule of thumb. Your gyro angle will not be exactly zero, but its value as calculated by the TDC will be very small. We dispense with precision in exchange for results. Where there are calculations there are errors. Rules of thumb are easier to remember and then you are doing the same thing every time. Repetition brings results. The extreme error tolerance of the constant bearing technique mitigates error. We're not trying to dazzle the world with fancy mathematics and false precision, we're trying to sink ships here.

Hold everything. Are you confusing the John P Cromwell technique, which uses the TDC with the Vector Analysis Technique, which doesn't? Because the Vector Analysis Technique needs speed set to zero, Angle on the Bow and range don't matter a bit (other than range has to be non-zero or the TDC goes wacko). You are setting the Torpedo Track Angle at the zero bearing and using your nav map as a vector analysis tool for the lead angle.

There are advantages and disadvantages to each. The most consequential error you can make with the vector analysis method is to do the analysis for one speed of your torpedo and shoot the other, for instance doing the lead angle analysis for a high speed torpedo then forgetting to set for high speed before you shoot. That can't happen with the John P Cromwell method because the TDC is changing your torpedo track angle automatically based on the torpedo selected. You don't even have to know the speed of your torpedo. With vector analysis that is critical. So only because of that I'd say that the John P Cromwell method is slightly more error tolerant.

[ColonelSandersLite]

Originally Posted by Rockin Robbins

Because the Vector Analysis Technique needs speed set to zero, Angle on the Bow and range don't matter a bit (other than range has to be non-zero or the TDC goes wacko). You are setting the Torpedo Track Angle at the zero bearing and using your nav map as a vector analysis tool for the lead angle.

Here's a hint for advanced users. Speed does not actually need to be zero. If speed is non zero and AOB *is* zero, and range is over like 1000 yards or whatever, this is still zero gyro in the TDC.

Why is this useful? I often attack convoys, striking 3 targets at once. Quite frequently, this involves one or two manually computed 0 gyro targets, quickly followed by one or or two targets handled by the TDC. In this situation, using the above leaves speed as one less thing I have to enter when I'm in a hurry.

[Rockin Robbins]

It is true that if AoB is zero speed cancels out. If you do it the same way all the time, though, fewer mistakes are made. So I say set both AoB and speed to zero every time you are sure to hit your mark.

Many of the details of my procedures are just error mitigation. Given that in a pressure situation errors will be made what procedures will make these errors inconsequential. Double covering options is one of those procedures. So is using the Cromwell method as opposed to vector analysis. So is arbitrarily picking a shoot bearing based on speed. It's all about error mitigation. People who love precision just HATE that. But all that counts is the BOOM at the end.

[ColonelSandersLite]

I also usually set speed to 0 as well. If for no other reason than it can be a pain to get that 0 gyro line perfectly straight using just AOB. Since speed has a hard stop at 0, it's just easier.

That being said, sometimes the time crunch in an attack means that you don't always have time to do everything you want to do. In this situation, the person who knows more of the ins and outs of targeting has the best chance of success.

[Rockin Robbins]

You must not have watched any of my videos or read any of my tutorials then. I can flatly state that with the John P Cromwell, Vector Analysis or Dick O'Kane techniques there is no time crunch. How can there be if the TDC is all set up half an hour before you shoot?

I assure you both are downright leisurely pursuits. Check out my Dick O'Kane Sonar Only Tutorial. The TDC is set up fifteen minutes before the shot. Did I say that yet another mechanism for error mitigation is to remove time pressure? All my constant bearing targeting techniques do that. No hurry, no errors. Assume there will be errors anyway and render them harmless. Simplify, toss out unnecessary calculation and steps, then do it again.

The simplest technique which can be performed in a leisurely manner leads to the most success. Time pressure is number one mother of error.

[ColonelSandersLite]

The answer to your question was two posts above. To reiterate:

I commonly find myself attacking 2 or 3 targets in a convoy simultaneously. Often the first and possibly second targets are a precalculated 0 gyro shot. The method doesn't matter matter here, there's no time crunch, use what you like (I do tables).

This is the key: The third (and sometimes second) targets are often not 0 gyro shots. In this case, if you want your 1st (target 1) 3rd (target 2) and your 5th torpedos (target 3) to all hit their targets simultaneously, there is a very substantial time crunch involved in getting everything reset to fire at the next target.

In this specific case, I find that it is very helpful to have the convoys speed with 0 AOB entered into the TDC before I launch torpedo 1.




Hmm... you know, I should really do a tutorial video on how to execute such an attack. I don't think there is actually a good one around.