The term flying-boat is used for the NC type because it is actually a stout seaworthy boat, that ploughs through rough water up to a speed of 60 miles per hour, and then takes to the air and flies at a speed of over 90 miles per hour. The hull or boat proper is 45 feet long by 10 feet beam. The bottom is a double plank Vee, with a single step somewhat similar in form to the standard navy pontoon for smaller seaplanes. Five bulkheads divide the hull into six water-tight compartments with water-tight doors in a wing passage for access. The forward compartment has a cockpit for the lookout and navigator. In the next compartment are seated side by side the principal pilot or aviator and his assistant. Next comes a compartment for the members of the crew off watch to rest or sleep. After this there are two compartments containing the gasoline-tanks (where a mechanician is in attendance) and finally a space for the radio man and his apparatus. The minimum crew consists of five men, but normally a relief crew could be carried in addition. To guarantee water-tightness and yet keep the planking thin, there is a layer of muslin set in marine glue between the two plies of planking. The wings have a total area of 2,380 square feet. The ribs of the wing are 12 feet long, but only weigh 26 ounces each. The tail in this craft is unique and resembles no other flying machine or animal. The tail surface is made up as a biplane, which is of the general appearance and size of the usual aeroplane. Indeed, this tail of over 500 square feet area is twice as large as the single-seater fighting-aeroplanes used by the army. ENGINES The four Liberty engines which drive the boat are mounted between the wings. At 400 brake horse-power per engine, the maximum power is 1,600 horse-power, or with the full load of 28,000 pounds, 17.5 pounds carried per horse-power. One engine is mounted with a tractor propeller on each side of the centre line, and on the centre line the two remaining engines are mounted in tandem, or one behind the other. The front engine has a tractor propeller, and the rear engine a pusher propeller. This arrangement of engines is novel, and has the advantage of concentrating weights near the centre of the boat so that it can be manœuvred more easily in the air. CONTROLS