Well, looking at the map I would have to go with you on the E-boat theory. It is definitly a nautical themed map. It is on a small scale which would go with a unit that has to operate in a specific region for an operation.

Are the circles with the dots in them bouys? I cannot read the picture well enough to try and translate it on the web.

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PEOPLE SLEEP PEACEABLY IN THEIR BEDS AT NIGHT ONLY BECAUSE ROUGH MEN STAND READY TO DO VIOLENCE ON THEIR BEHALF. GEORGE ORWELL