10th Patrol of U-53 - Radio Contact Intercept [Archive]

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XLjedi

09-07-07, 03:28 AM

10th Patrol of U-53
Sept 28th, 1940

Radio Contact Intercept Part 1

Time 14:53
Four days into our 10th patrol we get a radio contact from BdU. A lone ship is moving slow and heading in our direction.

http://xl-logic.com/mobo/patrol_reports/attack_20070906_01.png

Actually, it's not too far off our intended course. Like a gift... These are my favorite types of intercepts because the ship is playing right into my hands. I don't have to do any end-around or stationing plotting. I can procede on a direct intercept course and as I make contact at distance I'll be able to easily maneuver into my favorite 90° firing position as the target closes the gap.

I grab a screen print and pull the image into MoBo. After plotting my subs position and the contact position atop the nav map graphics I hover over the contact and press the "I" button to generate the intercept point.
http://xl-logic.com/mobo/patrol_reports/attack_20070906_02.png
Plotting a blue node on the intercept point and connecting to sub gives me a line that I can display the intercept bearing on. Hmmm... given our present speed of 9kts, looks like 259° is the course we need to take eh Wolf. Aye sir. Uh, that's Wolfgang my XO. Set course 259° speed 9kts for intercept.

Hmmm... 42 km away... it's 14:53 now... let's see 42km and 9kts should be like 4 hours or so traveling time? An early evening attack. Wolf double-check that.
http://xl-logic.com/mobo/patrol_reports/attack_20070906_03.png
Ooof! I guess I meant 2.5 hrs, bah! forgot about the knot to km conversion; too many hours without sleep. You should get some rest sir. So let's see it's almost 3:00pm, maybe around 5:30 we'll make contact. Wolf, have the cook prepare an early dinner... Seas are relatively calm, we should make consistent time/speed... and so should our dinner guest.

Time 16:20
BdU reports an update on the target position. Amazing the intel they have these days. We'll win this war in no time!
http://xl-logic.com/mobo/patrol_reports/attack_20070906_04.png
Hmmm... interesting, he's pretty much where we expected him to be. Wolf, that previous contact position was plotted at 14:50 can we get a speed estimate a little better than "slow" based on the new position at 16:20? I had assumed 6, but he's a little further along than I expected. Ahhh maybe it's my eyes... let's just confirm the speed. Aye sir.
http://xl-logic.com/mobo/patrol_reports/attack_20070906_04b.png
...for the distance covered in 1.5hrs I estimate a target speed of 6.1kts. Wolf yer killin me with the tenth of a knot. Let's just assume that tenth is just BdU position plotting error and make it an even 6. Aye sir

We still have an hour to go before we run into em... I'm thinking this might be a good opportunity for a submerged approach. At 1/3 speed we'll make 4kts submerged. Let's see if we can intercept from current position at 4kts.
http://xl-logic.com/mobo/patrol_reports/attack_20070906_05a.png
Mmmm... I like that approach angle. Take her down to 25 meters, maintain 1/3 speed, and set course 219°.

Navigator lay a course for 219°
http://xl-logic.com/mobo/patrol_reports/attack_20070906_06.png
This slower approach should get us in range in about an hour or so. We're going slower but we've cut the distance.

Time 17:15
Sir, hydrophone reports contact bearing 050° long range.
http://xl-logic.com/mobo/patrol_reports/attack_20070906_07.png

Time 17:20
Let's setup for an attack position at 1500 meters and 90° abeam.
Give me a 1500 meter radius...
http://xl-logic.com/mobo/patrol_reports/attack_20070906_08.png

Time 17:26
Let's adjust course for a 90° approach angle. Bring us up to parascope depth.
http://xl-logic.com/mobo/patrol_reports/attack_20070906_09.png

Time 17:38
Let's set the TDC for our known attack position. Wolf, double-check the attack scope and make sure it's still pointing at 0°, do not let the scope break surface. Aye sir, scope wire on 0°.
http://xl-logic.com/mobo/patrol_reports/attack_20070906_10.png
Come here Wolf I wanna show you something. Your solutions have been off lately. Let's review the process. Do you remember Fast-90?

Alright, TDC switch OFF...
Leave bearing pointing at 0°
Range = 1500 meters
AoB = 90° port
Speed = 6kts

For this 90° abeam shot I've set the attack scope pointing at a phantom ship bearing 0° on the targets path. The AoB in this case will always be 90° port or starboard. All you have to do is determine which direction the ship is headed. Conveniently enough, the AoB arrow points in the same direction as the ships heading. If the ship is approaching from your right the arrow would point to the left and vice-versa.

TDC switch ON

...the TDC is now calibrated! When you move the scope the AoB will adjust automatically. This allows you to aim at specific points and fire without having to reset the TDC. Works great on multiple ships that are moving along the same path (ahem, convoys).

(continued)

XLjedi

09-07-07, 03:30 AM

Radio Contact Intercept Part 2

Time 17:50
We're on station, set speed zero. Let's not give ourselves away; wait til the hydro bearing is reading about 30° before popping up the scope for a peek. Wait for it...
http://xl-logic.com/mobo/patrol_reports/attack_20070906_11.png

Time 17:53
...wait for it... good he's on about the 30° beam. Let's take a peek.
http://xl-logic.com/mobo/patrol_reports/attack_20070906_12.png

Yep, he's right where we expected him to be.
http://xl-logic.com/mobo/patrol_reports/attack_20070906_13.png

Yeah... just a little guy...
http://xl-logic.com/mobo/patrol_reports/attack_20070906_14.png
Make ready tube 1, depth 4, set pistol for side impact. Aye sir

Time 17:54
Open tube 1
Tube 1 open

I'm looking for a low gyro angle shot... let's aim for his stack and fire when it reaches the 20° bearing.
http://xl-logic.com/mobo/patrol_reports/attack_20070906_15.png
Notice how the TDC is adjusting itself automatically now for where I aim. With the scope pointed at 20° you can see the torpedo path is running nearly straight (close to 0-gyro angle). See how the AoB adjusted for my 20° bearing aim... it's like a whiz wheel AoB solver, I don't have to guess at it.

Time 17:55
Torpedo 1... LOS!

Time 17:56
http://xl-logic.com/mobo/patrol_reports/attack_20070906_16a.png
Torpedo Impact... YAAAAYYY!
Hmmmm, we were off a few degrees there to the stern. Wolf you might've been right about that extra tenth of a knot afterall. Ahead standard, surface the boat.

Time 18:03
She's going down sir...
http://xl-logic.com/mobo/patrol_reports/attack_20070906_18.png
Very good Wolf... stand down the gun crew. Note the time of sinking.

http://xl-logic.com/mobo/patrol_reports/attack_20070906_21.png

Time 18:05
http://xl-logic.com/mobo/patrol_reports/attack_20070906_20.png

Alyebard

09-07-07, 04:21 AM

A perfect interception course :know:, a nice shot :up: MOBO rules :rock:

Canovaro

09-07-07, 04:56 AM

A nice intercept!
It's always nice if a plan comes together :|\\ with or without the mobo (don't use it myself).

I have one comment though. A lone ship is always reported with speeds like slow or medium, unless BdU gives another contact report (like in your case).
This is the weak point of any calculation. You took 6 but the range could have been 4-7 or even greater.
What I do is calculate the position with a range of 7.5 when reported slow and then just wait for it. It's a bit dissapointing if it's much slower, but better than missing it altogether.
With convoys, you can always read the exact speed from the contact report...
There are a couple of other considerations as well. The contact report seems to be from 14:50. It is now 14:53. That's hardly any difference, but nexttime it may differ half an hour. It's just a matter of how quick you can get out of time compression.
You also don't want to cross the target's path literally, because it can spot you an start zig-zagging. you want to lay and wait submerged. The range of view depends of the time of day, the wind speed and fog. I would say it's max 7000 meter

I have made the convoy intercept 'theory' below which is based on some other basics that you can find on this forum, but has these things included in the calculation.

http://kuijperonline.nl/weblink/intercept.jpg

XLjedi

09-07-07, 08:39 AM

I actually used MoBo pretty sparingly on this one... I thought some folks might like to see how easy it is to calibrate the TDC without a lot of complex measurements or AoB guesstimates. I spent zero time on visual observations. I was setting up the TDC before I ever saw the target.

I have one comment though. A lone ship is always reported with speeds like slow or medium, unless BdU gives another contact report (like in your case).
This is the weak point of any calculation. You took 6 but the range could have been 4-7 or even greater.

For a "slow" report I'm pretty successful with 6. Setting it for 7 does usually give you some cushion. I wouldn't set it higher than 7 for slow.

The contact report seems to be from 14:50. It is now 14:53. That's hardly any difference, but nexttime it may differ half an hour. It's just a matter of how quick you can get out of time compression.
How fast you click TCx1 actually doesn't matter at all. In this case, I was pretty nimble, but sometimes I can be off by 30 mins. In which case I would just advance the target position for distance travelled in 30 mins by means of dead reckoning. Your intercept calculations are then based off the proper time adjusted position.

You also don't want to cross the target's path literally, because it can spot you an start zig-zagging. you want to lay and wait submerged. The range of view depends of the time of day, the wind speed and fog. I would say it's max 7000 meter

Rather than submerge and wait, I like to submerge and stay on the advance...

Notice I did submerge well beyond visual range. The first time the target had any chance to spot me was when I peeked the scope out of the water at 1500m and had the ship in my sights at a bearing of about 25°. At which point, I was opening tube 1.

Generally speaking, I try to station myself such that I can make the final approach submerged at 4kts regardless of which direction I'm coming from. So I try to intercept a station for a 4kt approach... not necessarily the direct method. As I mentioned, the initial stationing of this intercept is my favorite starting point because it decreases my workload by not having to plot an appropriate end-around.

I have made the convoy intercept 'theory' below which is based on some other basics.

Appears reasonable... :yep: The intercept was based on how I like to do it; but that was only half the story here. The other message I wanted to get across in this report is how easy it is to get started in manual targetting by choosing your attack position. In which case, all of your TDC dial settings are known.

That circle diagram you posted is pretty clever... I like it.

Canovaro

09-07-07, 02:07 PM

You also don't want to cross the target's path literally, because it can spot you an start zig-zagging. you want to lay and wait submerged. The range of view depends of the time of day, the wind speed and fog. I would say it's max 7000 meter
Rather than submerge and wait, I like to submerge and stay on the advance...

Notice I did submerge well beyond visual range. The first time the target had any chance to spot me was when I peeked the scope out of the water at 1500m and had the ship in my sights at a bearing of about 25°. At which point, I was opening tube 1.

Generally speaking, I try to station myself such that I can make the final approach submerged at 4kts regardless of which direction I'm coming from. So I try to intercept a station for a 4kt approach... not necessarily the direct method. As I mentioned, the initial stationing of this intercept is my favorite starting point because it decreases my workload by not having to plot an appropriate end-around.
I think both methods are equally effective.
I would proceed on the surface with higher speed and then dive at the final point. You would stay on the run while submerged the last part. :)

I have made the convoy intercept 'theory' below which is based on some other basics.
Appears reasonable... :yep: The intercept was based on how I like to do it; but that was only half the story here. The other message I wanted to get across in this report is how easy it is to get started in manual targetting by choosing your attack position. In which case, all of your TDC dial settings are known.

I think you made your point well! It's a good step-by-step.

That circle diagram you posted is pretty clever... I like it.
The circle diagram itself is not my idea...it comes from Dantenoc afaik :up:

looney

09-07-07, 02:59 PM

So for a slow contact speed is between 4 and 7?
medium 8 and 10 and for fast anything faster than 10? am I right?

XLjedi

09-07-07, 03:51 PM

Canovaro

09-07-07, 03:54 PM

XLjedi

09-07-07, 03:59 PM

So for a slow contact speed is between 4 and 7?
medium 8 and 10 and for fast anything faster than 10? am I right?
I like...

6 or 7 for slow (I favor 6)
8 or 9 for medium (I favor 8)

...and I've been guessing 16 at fast and haven't had much luck. Any recommendations there would be welcomed.

Fast can only be a tanker or a warship afaik.
A tanker I would guess 10 or 11.
Warships can be anything between 9 and...35? 40? I don't know. :lol:

Yeah I've also seen lone cruise ships hummin along at 16, but you're right about the tankers. Probably good guess for the Type IX cap'ns cruisin the Carribean.

When I've seen "task force" as the contact plot I've tried 16 and I haven't had much luck with that guess. Maybe 22? I think part of the problem is the blasted things are turning pretty tight patterns.

VipertheSniper

09-07-07, 04:52 PM

From what I've seen in convoys that travel fast they mostly do 12 knots, oh yeah anything over 30 (maybe even earlier, like 25) I think is displayed as very fast, only had that on escorts steaming full ahead up until now though. Medium goes from 8-11 knots if I'm not mistaken or more like 7.6-11.5 .

bigboywooly

09-07-07, 05:35 PM

[ContactSpeeds]
;less than each value means (in this order): stationary, slow, medium and fast speed ; over the last value means very fast speed
Merchant=0.1,8,12,35 ;[kts]
Warship=0.1,8,19,35 ;[kts] including uboats
Air=0.1,50,100,150 ;[kts]
Convoy=0.1,8,12,35 ;[kts]

So a merchant at slow speed can be anything from 1 to 7 kts
Medium speed 8 to 11 kts and fast 12 to 34 kts
35 and over is very fast - not something you will see from a merchant

looney

09-08-07, 02:47 AM

I came in contact with a fast mover (1939 still) was a tanker at 12 knots.

For slow I'll reckon 6 or 7 knots depending on angle of approach. Medium I always pick 9. Then again I never lived past 1941, so I don't know bout the faster merchants.

tnx for the numbers am glad my nlind guessing of the speeds werent that far of.

Canovaro

09-08-07, 05:13 AM