von Zelda

Draw a line representing the target course.

Draw another line from the target to your u-boat's position and then a few inches further.

Draw a circle from the target position with the radius equal to the speed of the target.

At the intercept point of the circle and the target's course, draw another circle with the radius equal to the speed of your u-boat (usually full speed of 16 - 19 knots depending on the weather).

Using the angle tool, look for the intercept point of the second circle with the line from target to u-boat. Measure the angle at this point using the line from the u-boat and a line to the intercept point of first circle and target's course.

Again using the angle tool, transpose this angle at the point of the u-boat with lines from the target to u-boat and a line from the u-boat toward the target course. This line is your new and accurate intercept course.

This method takes into account your current position relative to the target, the target's course and the ratio of the speed of target and the speed of the u-boat.

Hope this is helpful. It is very had to put into words so I hope you can understand it.