[DavyJonesFootlocker]

First off those S-boats are slow AND noisy. Generally getting fast warships is next to impossible, except if they are up close and personal and it's still a longshot. I was in a Porpoise-class boat and did come across a similar TF. It was night and lucky for me I was in a good position but over 10000 yards away. So I went to 2/3 speed submerged and somehow got withinh 9000 yards for my Mk.14 torps. I sent 4 on the Light Cruiser. first 2 were duds, next 2 WHAMMO!

My advice to you in an S-boat is to use it's slowness to creep into enemy harbors at night (preferably) and sink to your liver's delight. Also when you see a TF maybe check the speed and if too fast ignore attack orders. You never know you may need your torps and fuel for something else. Good position relative to a TF is important.