Modern day Submarine tactics

Hi Forum, I am a new member who just registered a few minutes ago.  I am a retired civilian and my experience with submarines is limited to shear interest in the subject, playing Silent Hunter III, and reading a few on-line documents especially regarding the type XXI U-boat.  I joined because I have a question about submarines tactics that I hope someone can help be with, so here goes.   As a layman my thoughts on how a real submarine attack would unfold is largely shaped by the typical Hollywood movie story line whereby one sub sneaks up on another sub and at the right moment launches a torpedo (Tigerfish?) and it's game over for the noisy sub.  The problem is, the instant the quiet sub launches it's torpedo, it gives away it's position.  Not that the hunted sub will be able to benefit from this information since it only has seconds to live.  But, if the hunted sub is one of a pack of 3 or 4 low cost submarines then the remaining pack of subs might well be able to deliver an effective counter attack.  So it strikes me that numerical superiority is the most important tactic for winning underwater battles.   Therefore it strikes me that the current approach of manned sub warfare is obsolete.