In the upper diagram the entering edges of the hydroplanes are inclined downward, and the force of the passing stream lines strikes upon the upper face of the blades. This exerts a downward force which causes the boat to sink, as indicated by the arrows marked "A, A." The opposite of this takes place when the forward ends of the hydroplanes are lifted. This brings the force of the stream lines against the under side of the hydroplanes, and the resultant is a lifting impulse in the direction of the line of least resistance, which is here indicated by the arrows marked "B, B." It is the lifting force so applied that makes it possible to raise hydroplane boats from the bottom even when having considerable negative buoyancy. [Illustration: ON PICKET DUTY This is a field of service to which the anchoring weights and the diving compartment of the Lake boats lend themselves conjointly with especial fitness. The illustration represents a submarine doing picket duty on an offshore station. A junction box is placed in a known locality with telephone or telegraph cables leading therefrom to the shore. The submarine, having taken her position on the surface, lowers her anchoring weights, reduces her reserve buoyancy to the desired extent, and then draws herself down to the bottom by winding in again on the cables connecting with the anchoring weights. Having reached the bottom, the diving door is opened and a diver passes out and makes the necessary connections between that junction box and the instruments in the boat.]