Did you by chance have your sub moving? You are supposed to go to all stop before launching a Mk.27 and then dropping deep if you can and staying that way until it hits a target on runs out.

I bet it picked up your props running.Mk.27s are very strange in game I have seen them latch onto target then hit the sound of another.I really on use them on pursuing escorts the louder the noise the better and you cant get much louder than a tin can at 27+knots. But they can and will target less noisy targets if nothing else is around.

My sub was moving at the time the cutie was set to a depth of 45meters but somhow missed the liner and came back at me.

I bet that is what got you then.The real Mk.27 was intended to be used against an attacking escort vessel which would have been running in at high speed and making lots of noise as well as heading directly towards the sub.

The cutie was not really "smart" per say meaning that it did not really lock on to a sound but followed the loudest noise it was able to pick up and had no way of knowing what it was tracking or if it had lost track of one sound(target) and was tracking another sound(target).It was based on an air dropped "mine" that was used against German U-Boats and they got the idea to modify it for use as a submarine launched weapon.But it was never intended to be used on a highly evasive target or against a convoy with multiple targets or a high speed target that was not on a direct course with the launching sub.

The USS Bard did once sink a small lone freighter with just a Mk.27 but they fired it from a pretty good depth and it came up and hit the hull from below direct contact like a finger pointing up at an angle something you cant really do in SH4 you can get a magnetic hit true but with the weak Mk.27 warhead a contact hit is much more effective.I am pretty sure that the in game Mk.27 dose not behave like a real one would have in certain respects.