It has nothing to do with being perpendicular to the target track (or 'fast 90' or whatever you want to call it). The range does not matter (much) if the gyro angle is close to 0. (within 10 degrees or so) In other words, if the torpedo moves pretty much straight out of the tube. If it needs to turn quite a bit then the offset position of the torpedo tubes from the periscope, together with the straight and circular section of the torpedo path will require it to turn a bit more than from the periscope vantage point. Especially if the target is near.
Setting the right speed is much more important to get a good hit. This is the prime factor in the amount of lead of the torpedo.
|