Figure 9. This graph compares the monthly number of U-boats available for patrol to the number of Allied vessels sunk by U-boats. Starting in 1942, the number of U-boats at sea (red line) increases, resulting in an increase in the number of Allied sips sunk (green line). By late 1942, the number of vessels sunk begins to decline. The user wanting a more detailed explanation can also learn that this point in time can be considered as the beginning of Allied technological ascendancy, which neutralized the U-boat threat, by selecting the Discussion button. (See colour figure at www.utpjournals.com/carto/kessler9.html.)