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Old 03-22-14, 04:33 PM   #38
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Default J.P.C. 45 Degree Method SHV Revised For Tutorial

Last updated 10th September 2017
This John P Cromwell 45
method adapted from imperial to metric for SH5 is very useful when used against convoys, especially if you are one of those gamers who like to get inside a convoy between the lanes.

Unlike the 90 shoot where you are in front of the first convoy lane and you want to get to a target in a different lane it is quite easy to hit the wrong target.

Another advantage with this method especially if you are using the G7e type torpedo is evading the escorts who will expect the attack coming from 90 and are likely to search for you in the wrong place which can buy you some valuable time.

The formula used is the same whether the targetís speed is 5 or 25 knots.
The 2 angles always remain constant as you will see as you use it.

Getting the Targetís speed using the 3 minutes and 15 seconds method.
1. Mark an X on the targets bow.
2. Run the 3 minutes and 15 second speed method.
3. Mark an X on the targets bow again.
4. Measure the distance to both X marks i.e. 600 metres = 6 knots.
5. Draw a line through both the X Marks to make a course (TCL) past the U-boat.
6. Place a 45 angle on the top of the TCL at a convenient place.
7. Move the U-boat on to 45 line if possible or parallel to it.
8. Use the Formula below for the attack.

This is the Formula used by making a separate diagram on the navigation map. This is for reference purposes only as this has already been done for you.
1. Draw the targets covered distance i.e. 600 metres.
2. Using the protractor place the 45angle so it rests on top of the end of the 600 metres nearest to your boat.
3. Take the Ruler and draw a line for the nearest torpedo range that you are going to use 1,700 metres.
4. The calculation is Torpedo speed Slow 28 knots x Targets speed 6 knots = 1,680 metres.
5. Place the ruler on top of the 45protractor angle and draw out 1,700 metres.
6. Take the ruler again from the other end of the 600 metres line and draw out so it reaches the 1,700 metres line.
7. Carefully make sure that each end of the line on the end the 600 metre line and the other end on top of the 1,700 metres lines is correctly placed.
8. With the protractor make an angle on top of the 2 lines = 12 (Starboard).
9. This 12 angle is used for setting the AOB.
10. Move the periscope until it shows 0 = 45
11. The firing point is 360 Ė 12 = 348 on the periscope bearing with the 2 Gyro dials vertical.
12. The AOB always starts at 45 whether Port or Starboard.
13. The AOB calculation is 45 - 12 = 33 AOB Starboard in this scenario.

Entering the data in the TDC.
1. In this scenario the target is coming from the left to right (Starboard)
2. The targets speed we know is 6 knots.
3. The torpedo speed is Slow = 28 knots for both G7a and G7e type torpedoes.
4. Enter the data in to the TDC with the periscope bearing on 0.
5. Enter the AOB as 45on the 0 periscope bearing.
6. With the TDC closed move the 0 bearing until you see both the 2 Gyro angle dials vertical.
7. The bearing showing is the firing point.
8. As soon as the periscope is moved the TDC will recalculate the new data automatically.
9. A range to the Target needs to entered in the TDC but has no effect in the solution.

Torpedo speeds (Multiply the torpedo speed by targets speed)
G7a 44 knots = Fast.
G7a 40 knots = Medium
G7a and G7e 28 knots = Slow

45 Attack Angle Attack > Targets speed based on 3 minutes and 15 seconds.

G7a and G7e Torpedo Speed Slow 28 Knots > AOB 45-12=33 Port or Starboard
Periscope Bearing Starboard >360-12=348
Periscope Bearing Port >0+12

G7a Torpedo Speed Medium 40 Knots > AOB 45-9ᴼ=36 Port or Starboard
Periscope Bearing Starboard > 360
Periscope Bearing Port >

G7a Torpedo Speed Fast 44 Knots > AOB 45-8=37 Port or Starboard
Periscope Bearing Starboard > 360
Periscope Bearing Port > 0

The easiest way to set your AOB is when the periscope bearing is showing
0and you can easily enter 45ᴼ in the AOB dial.
Port <-- is the target traveling from Right to Left.
Starboard - -> the target is traveling from Left to Right.
It is important that the periscope bearing needs to be adjusted until both of the gyro dials needles are vertical to give you the 45 shoot. (J.P.C. is an Imperial method converted here for Metric use.)

If you would like to see this method in action then there is a tutorial here although unfortunately the quality is not particularly good but you will at least see how things evolve.

Picture 1 > Setting out the convoy lanes.

Picture 2 > Setting the angle with the protractor.
The distance to the second convoy lane is 2,400 metres and is within the range for using G7e torpedoes.
45angle will put you closer to the first convoy lane, so you need to be aware if there is an escort close enough it may pick you up.
This is why I would advise using this method inside a convoy as this will maximise your potential.

Picture 3 > The periscope bearing is on
The AOB will be entered as -45

The convoy is moving from right to left = Port

Picture 4 > The speed 9 knots and range 2,400 metres have been entered in the TDC
The periscope and TDC bearing is showing 17
as it is being tracked.
Taking the target off being tracked and moving the periscope to the 12
firing position you can then fire each torpedo where you want it to hit the target as it crosses the periscopes cross hair.
The G7e solution is 28 knots x targets speed 9 knots = formula 252 (2,520 metres)
This has already been worked out as 12
is when the torpedoes are fired.

Picture 5 > G7e torpedo 1 impacting on the target.

Picture 6 >
G7e torpedo 2 impacting on the target.

Courtesy acknowledgement to RockinRobbins

Last edited by THEBERBSTER; 10-04-19 at 11:00 AM. Reason: Replaced missing pictures
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