Tips & Tactics
Attacking your target
1) Intercepting your target
Your attack of your target, whatever it may be, requires you to ask some basic questions. Is the target escorted? Is the target armed itself? What time of day is it? Are you in deep water and if so, at what depth is the thermal layer?
Now that you have answered these basic questions, how should you attack? Unless the target is a slow, lone and unarmed merchant vessel, you should use the "End-Run" tactic to intercept the target. Using the diagram below, you can see the position of your submarine to the enemy convoy. Using the End-Run tactic, you would run a high-speed course parallel to the convoy's. Once ahead far enough of the convoy, you will change course to get to a position where you can cut the engines and lie and wait for the convoy to come to you. You MUST get to the interception point before the convoy. More importantly, you want to do so UNDETECTED. If the escorts spot you, the merchants may scatter and the destroyers will certainly attack. In this case, all may be lost.
2) Torpedo Attack
For the most part, you can forget the "One ship, one torpedo" attack method that you may have used in previous submarine simulations. Many ships require you to hit them with at least two torpedoes. However, keep in mind the progressive damage that fire can cause. If you hit a target with only one torpedo and it remains afloat and burning, you can bet that the fire will progress and eventually destroy the ship for you. If the target's crew succeeds in putting out the fire though...you will be forced to sink it with another torpedo or shells from your deck gun.
If your target is a slow merchant (under 10 knots) then you won't have to worry about offsetting your torpedo shots normally. Just shoot with the settings that the TDC gives you when your solution reaches a point near 100.
If your target is a fast merchant (10+ knots) or another ship traveling faster than 10 knots, you will have to offset by one or two degrees in the direction that the target is moving. Usually a spread of torpedoes works well in this situation. Set the first torpedo with a two degree offset and the second torpedo with a one degree offset. You will get at least one hit on your target nearly every time. Targets traveling faster than 16 knots will need anywhere from a two degree offset to a five degree offset.
Coordinate your torpedo attacks if at all possible. By this I mean, don't fire at the nearest target and then shoot at another far away simultaneously. Many times, after one ship gets hit the rest of the convoy will change course. This will cause your torpedoes to miss most times if they are already on their way. Shoot at the distant targets first. Then, when the time remaining to impact is equal to the time to hit your next target with torpedoes, fire away. This way, all your torpedoes will impact at just about the same time and will increase your success rate.
3) Deck Gun Attack
The deck gun of the submarine was normally used for finishing off crippled targets or to damage faster targets enough so that they would slow down enough to allow the submarine commander to attack them with torpedoes. You should follow this doctrine as well. It is possible to destroy a target entirely with a deck gun but you will probably use up a lot of shells in doing so.
The AI is pretty good at using the deck gun. Just lock up a target and order "Man deck gun" and you will score many hits without much effort.
Beware using the deck gun on convoys. Some merchants may be armed with deck guns of their own. A lone armed merchant may not pose too much of a threat but a group of them could spell disaster for you.
By all means use the deck gun if you are forced to surface. Make destroyers your primary target in this case. Attempt to damage them to a "Heavy damage" state and then switch to the next destroyer. Destroyers with a "Heavy damage" state will have their guns out of action (beware that they can still ram you!) and are sure to be on fire most of the time. If they are burning, they may end up being destroyed by the fire. Take note that the destroyers have better damage control teams and will be more successful at putting out fires than the merchants.
Don't count out your AA gun while attacking. Though meant for defending your submarine from air attack, the shells from this gun can cause light damage to unarmored merchants and start fires on them as well. Bear in mind that it may take many shells to do so. On armored targets, you may as well forget using the AA gun on them.
4) Environmental Conditions
Many German u-boat commanders preferred to attack at night on the surface. This gave them greater maneuverability and increased visibility of the area. This hindered them in the later years when RADAR came into existence and got better with increased technological research.
Heavy seas and bad weather can make surface attacks almost impossible sometimes. In these cases, you may make better headway underwater where the waves won't hinder your speed. Also, you will get a better contact report by sound than visual sightings in this event.
Beware of attacking in heavy fog as well. This can be very dangerous as well as nearly impossible to conduct a successful attack. Heavy fog can hide enemy ships and you may not be able to see them until they are right upon you. If you happen to be in their path, you could take serious damage from being rammed.
Tips & Tactics
Normally, when a destroyer makes a run at your submarine, you would dive as deep as possible and run as silent as could be. However, try this tactic that I've found to be extremely successful in avoiding depth charges. You may incur some damage though it will be slim if any at all. Rest assured that you will fare far better than diving down and trying to hide in most situations. To be truly effective, you must be at a deep depth (between 100 - 150 meters) before the destroyer drops charges on you. When the destroyer drops charges on you, order periscope depth and flank speed simultaneously. As you do this, order your rudder hard over away from the path of the destroyer. You will avoid most if not all of the charges about 95% of the time if you do it right!!! After a while, the destroyers will run out of charges to drop and life will be much easier for you.
If you have a ship that is heavily damaged/dead in the water/destroyed and burning, try to steer a course to stop your sub right next to it underwater if you are being pursued by destroyers. They will avoid the crippled ship (there are them few that stupidly ram the crippled ship) and you can safely counter-attack from that position. Beware if the ship you are hiding by is destroyed as it may start to sink on top of you!
If the destroyers don't have you pinpointed, you can head for the bottom and run silent. Cut your engines and drop slowly to the seafloor. You might pass under a thermal layer which will help you as well. This has worked for me a few times but not all of the time. If they have you pinpointed though, they will drop charges on you and then you might be a sitting duck!
2) Periscope Use
Your periscope, if not used properly, can easily give your position away in a heartbeat. Almost as a rule in Silent Hunter II, NEVER use the PAGEUP key to raise your periscope. This will extend your periscope to it's fullest extent and would be like waving at light to your not-so-friendly destroyer opponent ... saying "I'm over here!!!" More so, if the destroyer has radar! what you want to do, is go to F2 and manually raise your periscope to a point to where it breaks the surface and the waves wash overtop of it. This will allow you to see your targets and minimize your exposure to the surface forces.
Limit your time that you have your periscope raised in battle. In WWII, most sub commanders didn't have their scopes above surface more than 10 seconds at a time. The longer that you have it up, the greater the chance that it will be seen.
Be wary of having your periscope raised while running at high speeds. In real-life, this would cause a very noticeable wake behind your periscope. I haven't seen this come into play in Silent Hunter II as most of the time it is the destroyer's radar that spots it. Also, I never go more than 1/3 speed with my scope raised...that's just me.