Firing a salvo at multiple targets

[RoaldLarsen]

Originally Posted by Pepe le Moko

Yes the later, i want to be able to fire a torpedo at several ships in a convoy, empty all my tubes then dive and try to escape.

Let's say you plan to launch the torpedos at the main target when it reaches the 0° bearing, right in front of your U-boat and you also want to fire at the ships that are in the same column in the convoy forward and aft of the main target. That means you have to work out the range for all the targets beforehand, right?

For instance, you have worked out that the range for the main target will be 1km and the ships in the column are 500 forward and aft of this main target, you cant launch the torpedos at the main target then pause and find the range for the secondary targets, you have to know this beforehand? If they are in the same column, it probably won't be much different but still...

Now if you want to fire at ships that are in a different lane or column, how do you make it so the torpedos hit their targets, roughly at the same time?

Firing at three or more different targets in the same column in a single salvo makes a lot of work for you. To get hits on multiple targets, you need to have an accurate reading for target speed, but all the ships in a convoy should be travelling at the same speed, so you only need to get that reading once. Where the extra work comes in is you will also need accurate range for each target that you fire at with a gyro angle other than 0. This must be the range to target at the instant of firing.

It is not easy to work out the range for multiple targets in advance, though if you know which column they are in, and your boat is stationary, I suppose it can be done. However, to use predetermined ranges, you must also have predetermined gyro angles. The more the gyro angle differs from 0, the more important it is to have a precise range reading. If you are waiting for targets to come to predetermined gyro angles, why not wait until they are at gyro angle 0, and skip measuring range?

You can make things a bit easier for yourself by having one or more targets that you dont need to get the range for. If you fire at a target when the gyro angle is zero (not the target bearing, you don't want to be shooting at something that is directly in front of you unless it is not moving.), it doesn't matter what the range is. So if you must fire at three or four targets in one column, I'd suggest firing at two or more when the gyro angle is at 0, perhaps with one or two other targets in between. The downside of this is that it takes a considerable amount of time between the first impact and the time you can make your second shot at gyro angle 0. For an 8 knot convoy with 500m spacing, and a range to target of 1000m, you have to wait more than a minute after the first impact before you can fire the last torpedo.

I rarely fire at more than two targets in a single column with the forward tubes, as it requires too much exposure to get all those required range readings and/or too much waiting around before the final shot.

There is a much simpler and safer way to attack multiple targets. Use fast 90 shots on different ships all in the same row. This way you don't need to know range to target at all, just course, speed and spacing. Assume an 8 knot convoy with 500m spacing, and sub stationary and perpendicular to convoy course at least 350m from track of closest column, with TDC set to fire with zero gyroangle, synched to scope, which is stationary at 15 degrees bearing. You fire an electric torpedo straight ahead when the ship in the fourth column from you crosses the crosshairs, drop your scope and fire another electric torpedo every 32.7 seconds. All four torpedos will impact at the same time. If you don't know spacing, you'll have to sight each shot, to be taken when the respective target is at 15 degrees.

That's the theory. I've never actually done this, because by the time I figured it out it was too late in the war to be getting good looks at ships four columns away. Also, I don't like my sub to be stationary. I prefer some forward motion so I can get away faster. Forward motion delays the subsequent firing times however.

My typical convoy attack in '43-'44 involves 1 fast 90 with electrics and one ranged non-zero gyro angle shot with steamers on a close target. Sometime I will make two fast 90's on adjacent columns, with a ranged shot in between. If visibility is such that I am not worried about steam torpedos being spotted, I may fire my first of two fast 90s with steam and my second with electric to minimize the time between firings.

With hedgehogs out there, I figure I might not get quite as many sinkings per salvo this way, but I will get a lot more salvos, because I won't get sunk. It has been 86 patrols since I was sunk by a convoy escort.