The U-boat Positional Grid System

U-boats had a novel method for reporting and receiving positional information based on a grid system. This was easier to use than the conventional latitude/ longitude fix and less liable to error in transmission. Each area of the world was divided into sectors which were given a 2 letter designation. For example, the sinking of SS Port Hunter (dispersed from OS.33) was reported as grid reference DG6397, referring to the sector designated DG on the main chart (below). Each sector was divided into a 3x3 grid which was further divided into another 3x3 grid to produce 81 sub-sectors which were given a logical 2 digit number (bottom left). Thus, the position of the Port Hunter is seen as DG63. The sub-sectors were similarly further divided (bottom right) to identify the final position of DG6397.
Atlantic chart showing grid sectors
(X=DG)
large chart of Atlantic
Detail of Sector DG (X=DG63)

Sector detail		 Subdivision of sub-sector DG63 (X=DG6397)

sub-sector detail