The French began experimenting with bomber designs in 1915. The Morane-Saulnier TRK and Voisin Triplane prototypes of 1915 and 1916 were not successful. The Voisin design was unusual in having a subsidiary tail boom above the fuselage, helping to support the empennage. French triplanes had more success in the long-range maritime role. Labourdette-Halbronn produced a twin-hulled triplane torpedo bomber prototype, the H.T.1, in 1918 and two prototypes of a modified H.T.2 version in 1919. Besson designed several triplane flying boats between ca. 1917 and 1919, initially in partnership with Levy. The Levy-Besson Alerte of 1917 featured a central wing of greater span than the others and many examples were used for ASW and patrol duties. Their last such design, the 1919 Levy-Besson High Seas had the top wing extended to the same span as the central wing and was also ordered into production, although the run was cancelled after relatively few had been delivered. Besson split from Levy and created his own Besson LB maritime patrol flying boat in the same year, and also the Besson Hydravion école which he exhibited at the Paris 1919 Air Show. He later developed a number of smaller designs for other roles, including Besson H-6 mail plane flown in 1921.