DTT against a destroyer if you let him get within 1,000 yds or less is almost 100% gonna kill him. Also the Mk.27 homers those can be highly effective if you use them correctly. I almost never attack escourts in a convoy I kill the merchants and I think it saps morale when I can kill you but you cant stop me they live and die by my will not thiers always fight on your terms never on thiers.I like to take down a lone patroling warship though. so thier last transimssion will be "HEEELPPP!!"
With the TC use that as fast as you want out of Pearl Id just keep it below 2000 after midway and once something is within spotting range dont use it at all then even a little TC might make you miss a change in direction or some other vital data TC also tends to make your sonarman forget to update you with data. Another thing when see a long range unknown contact along with the direction it will say slow medium or fast(very fast is always an aircraft) you can use this to plot just draw a "highway"(two spaced lines) in the said direction make it about 25 knm long then for slow guess 6 knots meduim guess 12 knots fast guess 20 knots then you know about how long that target is going to take to tarvel a given distance then you just plot your course to intersect a few miles ahead so your waitng when you get there it is best for you to travel at ahead flank that will give 20-21 knots in all subs but the S-boats and then it is about 13knts with Casey Jones on the steam.
Also when you dive dont travel at high speeds they will hear you from a mile away that is why you want to try to get into the best place before you dive and then silent run slowly it takes some time to learn this dont let some of the "experts" on this site make you think they had it all figured out(none of the guys that posted here so far act that way but some members do).It took me 3 months or so to get this down pat good enough I have had SH4 for 2 years I guess. I learn something new and tweek my skills every time I go on patrol.Another thing most wont tell you is the best way to learn allthe tricks is read what people do on this site read things in books and then take that bag dump it out and add your own ideas into the mix. Be like Bruce Lee make your own system.