Flying Boats for Navy Patrols, 1917-1934
When the United States entered the war, the Navy looked for a single-engine flying boat which could be put into production more quickly, take up less shipping space, and use shallow water. Curtiss offered the HS-1 (for Hydroplane, single-engine) in July 1917 with an America-style single-step wooden hull and a 200-hp Curtiss VXX eight-cylinder engine between the wings.
Copied from the R-type seaplane, the wings had an RAF-6 airfoil and three pairs of interplane struts on each side. When the 360-hp Liberty 12 first became available for tests, the Curtiss prototype was flown as the HS-lL (for Liberty) on October 21, 1917, and all production aircraft received this engine.
The first HS-ls were delivered to NAS Hampton Roads in January 1918, began service at Miami in March, and eight became the first American aircraft shipped to France, arriving on May 24. American Navy pilots in France had been flying their first patrols in French Tellier and Donnet-Denhaut flying boats until the HS boats were ready to begin patrols on June 13, 1918.
The three-seat HS-lL was armed with a Lewis gun in the front cockpit and two 180-pound depth bombs under the wings. To increase the lift so that heavier loads like 230-pound bombs could be carried, the wings were increased twelve feet in span, a fourth pair of struts were added on each side, and the rudder enlarged. This version became the HS-2L and most of the HS boats in production were completed or converted to this standard.
The first recorded attack by an HS boat on a submarine was that of July 21, 1918, on the U-156 off Cape Cod, but the bomb was a dud, and there is no evidence that other incidents were much more successful. Ten Navy Air Stations (NAS) in France got 182 HS boats during the war, but most served on the American east coast or at San Diego, then the only west coast NAS. A 110-pound wireless transmitter was sometimes carried, but carrier pigeons were more often used for emergency dispatches.
Navy demands for the HS boats were too great for Curtiss to build in its Buffalo and Garden City, New York, factories, and other firms became involved in that work. Between January 4 and December 27, 1918, Curtiss built 674 HS boats. LWF added 253 from June 1918 to February 1919, while Standard built 138, and Gallaudet 60. After the war, Loughead was allowed to assemble two in January 1919, Boeing added 25 by June, and 24 were erected from spare parts at naval air stations.
Many HS boats were sold to private operators in America and abroad after the war. Modified hulls and wings were tried on four HS-3s built by Curtiss in 1919, and two more HS-3s reworked at the Naval Aircraft Factory in 1922 had wing frames of steel tubing designed by Charles Ward Hall. These reduced empty weight about 10%, improving performance.
Liberty engines on Navy flying boats were low-compression versions whose shorter piston stroke sacrificed power to gain less-troubled engine reliability and endurance. High-compression models were sometimes used after the war.
Curtiss also delivered the first twin-engine H-16 on February 1, 1918; a larger H-12 development with a two-step hull and heavier armament. Britain ordered 125, and fitted the 75 that were actually shipped with 345-hp Rolls-Royce Eagles, but 124 Curtiss H-16s for the U.S. Navy had 400-hp Liberty engines. On November 20, 1917, an order for H-16s had been given to the new Naval Aircraft Factory (NAF) in Philadelphia and 150 were completed between March and October 1918. The first NAF H-16 flown March 27, 1918, was forwarded to a Navy station in England, and differed from the Curtiss model in detail, since plans had been redrawn to expedite production.
Armament of the H-16 included four 230-pound bombs, and four or five Lewis guns- one or two in the bow, one in the rear cockpit, and one at an opening on each side of the hull. The H-16 cost $37,850, compared to $16,900 for each HS-2.