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Robert H. Ferrell, Woodrow Wilson and World War I, 1917-1921. New York: Harper and Row, 1985, p. 35—
Having [to] resort to lookouts only when searching for victims, the U-boats [German submarines] enjoyed the advantage of a thin silhouette. Moreover, the U-boat lookout could see the masts of a steamer as far as fifteen miles whereas the steamer’s lookout could discern the sub only at four. The Allies camouflaged their ships by painting weird triangles and lines over the hulls, lending a circus aspect to every harbor.
