This is my latest and most successful tactic.
First, and often the most difficult exercise is to make contact with the convoy.
Maneuver to attain a position ahead of the convoy. This is probably nothing new to experienced Kaleuns. Since you have been running on the surface for quite some time to get ahead of the convoy your batteries/O2 should be at full capacity………you’ll need it.
It is essential that you are directly in front of and in the path of the convoy. A quick submergence to periscope depth for a sound reading is required for your positioning. Repeat as necessary.
Being in the path of and directly in front of the convoy is the key to this tactic. Adjust course so your heading is the reciprocal of the convoy heading. Maintain this course on the surface.
Once you are confident of your course you can remain on the surface until the WO reports ‘ship spotted’. Dive to 60m immediately. Worry not about being detected at this range. I wouldn’t order a crash dive, but a 7.0 kt dive to 60m has never been a problem. Once at 60m reduce your speed to 3.0 kt and initiate silent routine. Because you are heading toward the lead destroyer, which is always at the front of the convoy, your sonar signature is very small. Patience and nerves of steel are required because the lead DD will often approach very close aboard.
Because you are maintaining a watch on your hydrophone you will know when the lead DD has passed. I usually give the DD 3 minutes after passing before I order a move to periscope depth, all the while maintaining a silent routine. On occasion the lead DD will turn hard about and make a run back to the convoy so a well maintained watch on the hydrophone is critical. If the DD is headed back at you stop you accent until the danger passes, and it will unless you lost your. patience and nerves of steel. Continue your accent to periscope depth.
Because of how you positioned yourself you should be heading towards the heart of the convoy. Yes, that is where all the major targets are located. None of those low tonnage small or coastal merchants, the big boys, T3, T2, C3, troop transports, and an occasional passenger liner, is what you are after this time. Adjustments to your heading may be necessary to put yourself in the best position between columns. Be advised, never allow yourself to become fixated with your periscope above the waves for longer than a few moments, remember the lead DD may not be far behind you. Pick your targets quickly. Also during rough weather watch your depth very closely. Nothing will give your position away more quickly than a broach. Fifteen meters will keep your conning tower below the waves and still allow for some quick target acquisition.
My patrols are performed in the type VII boats. Consequently I have only five fish available for the attack, which is how I will explain the attack. If you are commanding the type IX or XXI your boats and attacks will allow for more weapons. Initially I pick three targets. The largest tonnage is what I’m after so I pick the biggest ships. The targets may be on my port or starboard sides. I always choose one ship to attack using my aft tube. That ship is as far at the head of the convoy as practicable. The aft target is very important. You see the lead DD will always go toward the closest and last ship hit by a torpedo, and the lead DD is your greatest threat.
Because of your position, within the convoy, the gyro angles and the angles on the bow will be very high. This can be a bit un-nerving if you are not accustomed to it. Your advantage is the close range. Choose your targets in an order which brings the least attention to your position.
That is, the largest ship that is ahead of you and furthest away that is 1000m or less. Your second target will be on your bow or less than 90°/270°angle about 600m away. Always use your stern fish last.
During poor weather, with silent routine off, you may be able to have one reload and attack before the DD’s localize your U-boat but don’t count on it and be ready to dive quickly.
For the escape I dive at 7.0 kt and maintain my reciprocal heading until I reach 80m. The noise of the dieing ships will keep you hidden for a short time. At reaching 80m I revert to silent routine and keep a close watch on the hydrophones. Knowing where the DDs are will help you evade, attempting to keep the lowest possible cross section to the DD’s sonar. Course changes of 10°every 5 to 10 minutes will also help in your evasion.
That’s how I do it.
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