But their ships did sail on a globe and not on a Mercators projection. The Grid Map is clearly a Mercator's projection and such a projection has limitations for navigation. The shortest distance between two points on a Mercator's projection is, as can be seen on the Grid Map, a straight line, whilst on a globe it is a curve.
I believe there must be an additional book for use with the grid Map which gives the Latitude and Longitude for the center of each Grid Square.
From the U-Boat Grid System
http://www.convoyweb.org.uk/extras/inde ... htm~exmain;
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"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."
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From this we can see that conventional navigation was side stepped in order to find a quick and certain way of
transmitting a U-Boat's position. AK55 is much quicker to send than; 56* 20' N by 36* 20' W.
The grid system is not about navigation but is a method of reporting. So if the actual position of a grid square is needed then the lines between physical locations on an actual globe are needed.
I am going to attempt to plot all positions by Latitude and Longitude which were reported in War Diaries, Sighting Reports and from Personal Diaries, during the life of this operation. This may take some time, but it may tie up the loose ends. Then possibly we'll get a clearer picture of what went on.
Doenitz and his U-Boats may not have use Google Earth, but Doenitz most certainly used a globe at U-Boat Headquarters, so as to be able to make sense of U-Boat reports.