[Pisces]

Yes, but the further out the target is, and the shorter his length, the better you need to know his exact speed.

Take his length, and divide it by the range, i.e. 95 yards at 3000 yards is 31.7 yards per 1000 yards. 1 degree is 17.5 yards wide at a 1000 yards distance (same values apply if you use meters instead of yards), so the ship is 31.7 divided by 17.5 = 1.8 degrees wide. If the TDC aim is off by halve that angle (=0.9 degrees) then you risk missing the target if you aimed at it dead center.

So how do you know how accurate the speed must be? First you need to know how to convert speed to the lead angle.

The lead angle is based on the target speed, the speed of the torpedo, and the AOB of the target.

The formula is:

lead_angle= arcsin( Target_speed x sin(AOB) / Torpedo_speed )

(sometimes the arcsin button on a calculator is shown as "sin with superscript -1" or "inv sin" or "asin", or if you want to avoid that and allow yourself some inaccuracy simply multiply with 57.3 to get degrees. But this only works because lead angles are generally speaking quite small. You can't avoid the proper arcsin button on your calculator if the angle is more than 20 degrees)

Let's say for example, it has 90 degree AOB ( sin(90)=1 ), 10 knots speed and the torpedo moves with 31 knot:

lead_angle = arcsin( 10 X 1 / 31 ) = 18.8 degrees

(or 57.3 x 10 x1 /31= 18.5 degrees, ... and notice this simplification already cost you 0.3 degrees in accuracy)

The lead angle is roughly proportional to target speed. That means if target speed is actually 5% faster than 10 knots (so 10.5 knots), then the required lead angle is also about 5% more. (with our example: 19.8 degrees is required for 10.5 knots) Do you see the difference? 1 degree. If you thought it was doing 10 knots but in actuality it moved 10.5 knots, then the torpedo would pass behind the target. Because the stern is 0.9 degrees behind the center at that range. If it is further out, then the 0.9 degrees size would turn into a smaller value. And if the AOB is not 90 degrees, it's appearant size is even smaller. (times sin(AOB) )

You can easily get the speed wrong by 0.5 knots if you rely on the 3-minute plotting rule and use the 'crude' maptools (at those short track-lenghts). To get an accurate speed you need to average the distance over multiple 3-minute intervals.

As you might have noticed, a fast torpedo also help to reduce the lead angle, and limit the aiming error based on speed.