In 1916, the Navy reviewed its procurement of flying boats. The service had on hand large numbers of the little F Boats and orders had already been placed for the giant H Boats. A gap existed. There was need for a coastal patrol flying boat larger than the little F Boats, yet smaller and less expensive than the H series. A flying boat was required that had reasonable endurance while on patrol along the coast in search of U-boats, yet was cheap enough to order in large quantity. Thus was born the Curtiss HS boats.
The letter H referred to the large patrol aircraft series, while the S indicated that it was a single-engine design. The HS-1 was essentially a scaled-down version of the earlier twin-engine H models. The original powerplant of the HS-1, which was introduced early in 1917, was the 200 hp Curtiss V-X-X, an eight-cylinder water-cooled V-engine, but that proved to be too small for the HS-l. On October 21, 1917, the HS-1 was used as the test-bed for the first flight of the new Liberty 12 twelve-cylinder water-cooled engine, which in its original form developed 350 hp and was destined to become the major American aeronautical contribution to World War I and one of the world's great aircraft engines.
Following the successful marriage of the HS-1 airframe and the Liberty engine, the Navy ordered the HS-1 into large-scale production as the Navy's standard coastal patrol flying-boat. The numbers required were beyond the capacity of the Curtiss plants at Garden City, Long Island, and Buffalo, New York, so that a number of aircraft firms received orders from the Navy: Lowe-Willard-Fowler, Standard, Gallaudet, Loughead (later renamed Lockheed), Boeing, and the Naval Aircraft Factory. The Boeing versions could be distinguished from all the others in that they were fitted with horn-balanced ailerons only on the upper wing. The others had ailerons on both wings.
After the HS-1s, by this time designated HS-1L to identify installation of the Liberty engine, had entered service, it had been found that the standard 180 lb (82 kg) depth-bomb was ineffective against submerged German submarines prowling off the American east coasts. Since two of these were all that the HS-1L could carry, it was decided to increase the wing span so that heavier 230 lb (104 kg) bombs could be carried. The modification was quite simple, an additional 5 ft 5.75 in (1.67 m) panel was fitted between the centre section and the regular outer wing panels, and transforming the three-bay wing into a four-bay wing. Defensive armament consisted of a single flexible 0.30 in (7.62 mm) Lewis gun
This modification, which resulted in a new designation of HS-2L, was made to the majority of aircraft still on order, and there is no distinction in serial numbers between HS-1Ls and the HS-2Ls. The USN flew the type on anti-submarine patrols from bases at the east coast of the USA and from Nova Scotia, Canada. They also were the first American-built aircraft received by the US Naval forces in France, eight arriving by ship at the US Naval base at Pauillac on May 24, 1918, while the first flight was made on June 13. Records indicate that 182 HS-1Ls and HS-2Ls were distributed among 10 of the 16 Naval Air Stations in France. Of the total, only 19 can be confirmed as HS-2Ls. The HS-2L remained the standard single-engine patrol and training flying-boat in the post-war years, examples remaining in the inventory until 1926.
The HS-3 was an improved model with revised hull lines under development at war's end, Curtiss built four and the Naval Aircraft Factory two. By the end of the hostilities 126 HS-series aircraft out of 1,143 ordered had been, or were cancelled. Subsequently twelve HS-2Ls were donated to Canada, and many were acquired by civil owners in the USA and Canada.
For Canada the HS-2L was a real pioneer aircraft, it became its first bush aircraft, flew the first forestry patrols, made the first aerial timber survey, staked the first mining claim using an aircraft in 1920, and established the first scheduled air service, and the first regular air mail service in Canada. It remained the predominant Canadian bush plane until 1926 or 1927, and a few were still in use as survey planes in Canada in the early 1930s.
Curtiss, Garden City, Long Island, and Buffalo, New York: 675 HS-1, HS-1L, and HS-2L, s/n A-800 to A-815, A-1549 to A-2207 (A-815 cancelled), and 4 HS-3, s/n A-5459 to A-5462. Lowe, Willard and Fowler, College Point, Long Island: 200 HS-2L, s/n A-1099 to A-1398 (50 cancelled). Standard, Elizabeth, New Jersey: 150 HS-2L, s/n A-1399 to A-1548 (50 cancelled). Gallaudet, East Greenwich, Connecticut: 60 HS-2L, s/n A-2217 to A-2276. Loughead, Santa Barbara, California: 2 HS-2L, s/n A-4228 to A-4229. Boeing, Seattle, Washington: 50 HS-2L, s/n A-4231 to A-4280 (25 cancelled). Naval Aircraft Factory, Philadelphia, Pennsylvania: 2 HS-3, s/n A-5590 to A-5591.
An additional 24 HS-2Ls were obtained in the post-war years by assembling accumulated spare parts at various Naval Air Stations, and assigning new serial numbers to the complete aircraft:
NAS Miami Florida: 6, s/n A-5564 to A-5569. NAS Hampton Roads, Virginia: 5, s/n A-5615 to A-5619 (A-5619 cancelled). Lowe, Willard and Fowler: 1, s/n A-5630 (cancelled). NAS Key West, Florida: 1, s/n A-5787. NAS Anacostia, Maryland: 1, s/n A-5808. NAS Coco Solo, Canal Zone: 1, s/n A-6506. Naval Aircraft Factory, Philadelphia: 7, s/n A-6507 to A-6513. NAS San Diego, California: 4, s/n A-6553 to A-6556.