Proof?

I have used subs for quite some time. When i approach ships at OH submerged they veer away and start throwing HH at me. Also when using my BB i can see submerged subs some time even if there are no FF/DDs near us.

I agree with the second half of this. During a game, I've seen a sub appear and disappear while submerged and the only thing around was BBs. At first, I thought an AA ship must have had some crazy good sonar, but there was nothing even close. I don't know if its because of the SS overheating or maybe there is a hack or some other crazy thing.... but this is possibly true.

What you are seeing is the long range pick up from another friendly sub's sonar.

Often times I'll be motoring along and my sonar will pick up a sub. I won't necessarily chase him, as my mission is on towards a different target. But what you'll see is the Sub being detected by my sonar, then goes off when either the enemy sub or my sub move out of range.

Othertimes, a sonar will turn off when the sub, or destroyer is sunk that had the sonar displaying the sub.

Only CA and BB can't use sonarmen, but their escorts can. Some escorts have high level sonarmen on board and pick you up a lot further out than your torp range. As noted, there may be another sub in the vicinity that is providing sonar coverage for your team.