The motor-boat pushed off, swung round, and set off at full speed for the invisible shore; while Derek, after testing the contacts--a process that took what seemed ages of suspense to the impatient Brigadier-General--gave the word for the four motors to be started. Taxi-ing over the smooth sea nearly two hundred yards until sufficient speed was attained, the huge sea-plane "took-off" almost imperceptibly. Then, climbing to two thousand feet, the triplane settled down to her long flight to the distant shores of Spain. CHAPTER XXIX In the Interests of the State It did not take Derek long to accustom himself to the peculiarities of the sea-plane. Had it been one of the flying-boats that the Lieutenant had been called upon to pilot across the seas the task would have been an awkward and difficult one. Once fairly up, there is very little difference between an aeroplane and a sea-plane, but there are wide distinctions between the latter and the huge flying-boats which, devoid of floats, rely upon their hulls for buoyancy when on the water. Derek elected to fly fairly high, maintaining a height of five thousand feet. This gave him a chance, in the event of making a blunder with the unaccustomed system of controls, while at the same time there was less chance of coming across an air-pocket. Quickly he discovered that his hand had not lost its cunning. Although it was months--it seemed like years--since Derek had had control of joy-stick and rudder-bar, the old skill still remained. And the exhilaration of it! To be once more rushing through space, soaring high above the waves! "This is some stunt," thought the reinstated pilot. "Wonder what's taking the old Brass Hat to Spain? Joy-ride, or what? After all, it's all in a day's work." Applying the automatic steering device Derek turned to consult the charts. A hasty examination showed that his predecessor had faithfully recorded the course almost up to the time of the triplane's involuntary descent. The red-inked line and rough-pencilled notations were of considerable service. They enabled Derek to set a compass-course corrected for air leeway and ordinary magnetic deviation. Provided the force and direction of the wind remained fairly constant, the task of piloting the seaplane would be a fairly simple matter. It was aviation _de luxe_. The pilot's house, with windows of triplex glass affording an all-round view, was warm and free from buffeting draughts. With the glass in position the roar of the powerful engines was reduced to a barely perceptible purr.