To overcome the above-mentioned difficulties, Mr. Holland invented a device and was granted a patent (No. 492,960) for a triangular drag, which was expected to keep the vessel on a true course when under water. This triangular drag was the novel feature of Mr. Holland's 1893 design, and was intended automatically to steer the vessel on a straight course when submerged. It was intended to operate on the following ingenious principle: While the vessel was running on the surface the steering gear was under the control of the steersman. In this condition the compass could be adjusted, as the vessel was on a substantially level keel and the masses of metal remained fixed in their relation to the compass, but when the vessel was caused to dive the masses of metal changed their relation to the adjusting magnets and the compass was thrown out of true. Therefore, on beginning a dive the vessel was first started on the surface on the course it was intended to follow submerged until the triangular drag, being drawn through the water, assumed a direction parallel to the axial line of the boat by reason of the rush of water against said drag, and especially against the rib thereon. As soon as the boat was on her course the steersman was expected to disconnect his hand steering gear and allow the drag to control the rudder to hold her to her original course. Mr. Holland maintained that any departure from a straight line would cause the drag to produce swinging motion of a lever, which was expected to throw the rudder in a reverse direction, thus returning the ship to her original course. Another automatic steering device operated by the pressure of the water was expected to automatically control the depth of submergence, it being only necessary, theoretically, to move a control lever to a point on a dial corresponding to the desired or predetermined depth of submergence, and the horizontal diving rudder would then be automatically manipulated to incline the bow of the boat down so as to dive until the desired depth was reached and then to be manipulated to throw the bow up or down to maintain that depth. In further describing his 1893 design for the _Plunger_, for which he received the award based on a guarantee of performance, Mr. Holland describes her as follows: