The last of the RBVZ’s First World War fighters, the S-20, embodied lessons learned from licence manufacture of the French Nieuport 17. The production version, with a 120hp Le Rhone engine, was said by its pilots to be faster than the Nieuport, with a top speed of 190km/h; but only five were ordered, leaving the RBVZ free to concentrate on production of its Ilya Mourometz bombers.

Intended as a twin-engined fighter capable of inflicting heavy blows on enemy aircraft penetrating Russian airspace, the S-18 had a cockpit in the nose for an observer-gunner. Two 150hp Sunbeam pusher engines failed to lift it off the ground at its maximum weight of 2100kg.

During the First World War most Russian squadrons flew French-designed aircraft, many of them built under licence. Sikorsky’s single-seat S-13 and S-14 biplanes were probably not completed. Three two-seat S-16s were built as trainers for bomber crews of the Squadron of Flying Ships in 1915, followed by about twenty-four more as two-seat S-16-2 and single-seat S-16-3 bomber escort and reconnaissance scouts with 80hp Gnome engines in 1916-17. A machine-gun was mounted under the top wing, firing clear of the propeller, until Engineer Lavrov invented an interrupter gear for a fuselage-mounted gun.

For winter operation, a number of S-16s were flown on skis in place of the standard four-wheel landing gear; at least one was fitted with twin floats in 1916. Contemporary accounts show that pilots enjoyed the stability, manoeuvrability and delicate controls of the S-16s, but they were outclassed by German fighters of the time.