Curtiss designed series of aircraft 1907-15 including J and N series; eventually, features of both series combined the JN which culminated in JN-4D, the most widely-produced trainer of WWI. Curtiss engaged British designer B. D. Thomas to prepare J design based on a British Admiralty spec for their Type 137 biplane (see below). N design followed, differing only in detail from the J; best features of both combined in the JN design. 1916, Congress authorized creation of an air force, and Curtiss was ready with "Jenny" trainer. Curtiss and 5 licensees produced Jennies. Was developed into a number of important subtypes by installation of different engines or equipment. Most notable was JN-4H (H for Hisso) with 150 hp Hispano-Suiza engine; performance improved significantly. After the war, thousands of surplus aircraft sold to civilian firms and individuals. Dominated civilian market for 6 or 7 years afterwards. Availability, low cost, and forgiving handling characteristics made it very popular. Appearance throughout the country awakened people to aviation; became part of American folklore in early 20s. On the other hand, large number and low cost of surplus Jennies effectively killed market for new aircraft until mid-20s. New models did not gain a foothold until supply of surplus aircraft exhausted. Curtiss' decision to solicit help of English designer speaks ill of state of American aeronautics 10 years after Wright Brothers' first flight. Although Curtiss was leading designer and manufacturer in America, he was more comfortable with older A-frame designs than more modern designs appearing in Europe. 1912, he built Curtiss Military Tractor which along with versions built by Glenn L. Martin and Burgess Company were well received by the Army. Recognizing importance of a new trainer (with WWI approaching), was unwilling to take chance on a follow-up design of his own and therefore went to Europe (England) for help.