What made them drop depth charges?
 

This may have been asked before so forgive me.
I was playing a mission last night, reckless I know but I took on a DD that was heading strait for me, I fired and got it, then I notice two more further away but turning towards me.
So I decided to turn to port, then changed my mind and turned to starboard rigged for silent and went deep.
By the time the DD's got to where I sank the other one I was a good distance away but they circled that area looking for me, I was pleased I evaded them and kept going, I was under a thermal as well so I felt even more safe.

Now these two DD's went further away to the direction I first took and started dropping depth charges, so was it my first reaction to go to port that made them think that was where I had gone, and the main question what made them drop charges because I thought they dropped them on a sound contact or was it just lets drop some in case?

I managed to turn back to port further away and luckily got lined up with the convoy, I went to periscope and stopped all engines, I waited then managed to sink 3 more ships then decided to turn back to starboard and go deep again.
The end result was I failed the mission because I didn't sink all the convoy, but I thought I did a good job and escaped without any damage, if I had stayed I may have been toast because there were other escorts with the convoy.

Short answer
 

They were hunting a submarine that sank some of their boats.

:D:D Ha Ha yeah, I meant to drop them where I wasn't, I said in my above post I thought they only dropped them when they got some kind of ping or sound contact so was it a whale they killed lol?

Perhaps they're simulating the first DD that you hit, getting on the radio and going "You must avenge our demise immediately!!! He was headed East from us, about 800 meters out!!! btw, we need more lifeboats!!!", so that's where they went??? Of course, we've been noticing that the AI just gets confused as to which way is which sometimes, and that sometimes, Superman is helping them with his xray vision and super hearing and eye sight...

Just a thought, they head toward where you were, and probably heard you on passive sonar making that first turn. Then you get under the thermals, slow down and go another direction. Unless they pick you up again, they won't charge in on you, but keep trying to sink you where they think you are.

They are fishing

If they lose contact, they randomly drop charges where they found you, and also where they think you might be

I guess the thinking is a less experienced skipper might panic and turn on the screws, thereby revealing himself

This is what I have found:03: