Robert A. Kilmarx wrote several times to Sikorsky Aircraft seeking information on pre-revolutionary Russian aviation for his book A History of Soviet Air Power, published in 1962. This collection consists of three letters Kilmarx received in reply to his inquiries.

Igor Ivanovich Sikorsky (1889--1972) was born in Kiev and graduated from the Naval War College in St. Petersburg. While in Russia, he experimented with rotary-wing craft and designed the first multi-engined fixed-wing aircraft, the S-21 Grand and Il'ya Muromets. He immigrated to the United States in 1919 and a few years later formed the Sikorsky Aero Engineering Company (later Sikorsky Aircraft which became a subsidiary of United Aircraft and, eventually, United Technologies Corporation). The Sikorsky S-29-A and S-38 arrived to acclaim and use in air transport. In 1939, the Sikorsky VS-300, the world's first successful helicopter, was flown for the first time and by 1943, Sikorsky's company was producing the Sikorsky R-4, the world's first production helicopter. After many more years of achievement and a multitude of honors for his highly significant contributions to aviation, Igor Sikorsky died at the age of 83. Michael E. Gluhareff (1892--1967) was a pilot for the Imperial Russian Army during World War I, before leaving that country for Finland where he began designing aircraft and working as a test pilot. Gluhareff came to the United States and began working for Sikorsky Aero Engineering Corporation in 1924 as a draftsman and engineer. Gluhareff had a long career at Sikorsky which saw him promoted to Chief Engineer in 1942 and Engineering Manager in 1957. Gluhareff was well-known for his airfoil design and held numerous patents for aircraft designs as well as components including inventions relating to rotors and horizontal stabilizers. Robert A. Kilmarx wrote several times to Sikorsky Aircraft seeking information on pre-revolutionary Russian aviation for his book A History of Soviet Air Power, published in 1962.