Well actually you're doing it textbook style
Just keep in mind that patience is the key here (or anywhere else in SH3 for that matter
). Don't even try to increase the time compression! (A foolish error I made countless times. To be honest, I still make that error sometimes.). Be patient, stay deep.. well you obviously know the drill. Just wear them out. It's '39, they should give up relatively fast.
And keep your speed under 2 knots. That way they won't hear you. (You probably know this already but still) You don't even have to go into silent mode. Because all that does is prevent you from loading torps and doing repairs. So if you're not damaged or reloading, setting your speed at under 2 knots will have the exact same effect as running silent.