Bell Helicopter Textron. [Booklet: B8106.3A 409 Advanced Attack Helicopter], book, March 2, 1973; (https://texashistory.unt.edu/ark:/67531/metadc1831658/m1/9/: accessed July 16, 2024), University of North Texas Libraries, The Portal to Texas History, texashistory.unt.edu.; .