07/31/2011. Remarks by Johan Visschedijk: "Sierra Aircraft Industries Ltd., founded in 1928 at San Leandro, California, USA, moved to Modesto, California a year later. The company ceased operations the same year, after they had produced two examples of the Sierra BLW, designed by H. Sherman Tharpe. The assets were later bought by the Hawke Crop Dusting Company, formed by Edwin R. Hawke and John Cuneo at Modesto in 1931. Tharpe designed for Hawke a smaller version of the Sierra BLW, designated Hawke SJ (also referred to as Hawke Duster).

The Hawke SJ was a two-seat duster that could carry a hopper load of 1,000 lb (454 kg) and three examples were produced in 1931, the first (NR10609 c/n 1) by a 330 hp Wright radial engine, the other two (NR10626 c/n 2, NR10627 c/n 3) by a 220 hp Wright. NR10609 and NR10627 crashed and were deregistered May 15, 1941 and July 22, 1937 respectively. NR10626 was scrapped in 1945, although its registration was cancelled on April 6, 1948."