Early torpedoes espically Mk14's tend to run deeper than what you set them for.
Typically 10 feet deeper
Regardles of manual or 'auto' targeting.
Set them shallow and you will have better results.
The torpedo turning is the gyro angle and is normal behaviour and is required to intercept the moving target.
All the green triangle is really telling you is that the shot is within 'acceptable' limits of the gyro offset. When in fact the torpedoes are quite capable of much greater offsets of up to 90 degrees and possibly more.