Such apparently grotesque patterns aimed to distort the lines of the ship and to warp the perspective by which the course is estimated. This was the final type of marine camouflage at the close of the war. Besides relying upon these illusions, ships zigzagged on being attacked and aimed in other ways to confuse the enemy. No general attempt was made to disguise the bow, because the bow-wave was generally visible. However, attempts have been made to increase it apparently and even to provide one at the stern. In fact, ingenuity was heavily drawn upon and many expedients were tried. After low-visibility was abandoned in favor of the optical illusion for frustrating the torpedo-attack by the submarine, there was a period during which merely a mottled pattern was used for vessels. Gradually this evolved toward such patterns as shown in Fig. 92. In this illustration it is seen that the optical-illusion idea has taken definite form. During the period of uncertainty as to the course the pattern should take, a regularity of pattern was tried, such as illustrated in Figs. 93 and 94. Finally, when it dawned more or less simultaneously upon various scientific men, who were studying the problems of protecting vessels upon the seas, that the geometrical-optical illusion in its well-known forms was directly adaptable, renewed impetus was given to investigation. The scientific literature yielded many facts but the problems were also studied directly by means of models. The latter study is illustrated by Figs. 95 and 96, the originals having been furnished by Mr. E. L. Warner,[11] who among others prosecuted a study of the application of illusions to vessels. The final results were gratifying, as shown to some extent in Figs. 97 and 98, also kindly furnished by Mr. Warner. It is seen that these patterns are really deceiving as to the course of the vessel. [Illustration: Figs. 93 and 94.--Attempts at distortion of outline which preceded the adoption of geometrical-optical illusions for ships.] [Illustration: Figs. 95 and 96.--Illustrating the use of models by the Navy Department in developing the geometrical-illusion for ships.] The convoy system is well known to the reader. This saved many vessels from destruction. Vessels of the same speed were grouped together and steamed in flocks across the Atlantic. Anyone who has had the extreme pleasure of looking down from an airplane upon these convoys led by destroyers and attended by chasers is strongly impressed with the old adage, "In unity there is strength."