XA-21攻擊機 (Chinese Wikipedia)

Analysis of information sources in references of the Wikipedia article "XA-21攻擊機" in Chinese language version.

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3web.archive.org

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1books.google.com

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archive.org

Phillips, Edward. Stearman Aircraft: A Detailed History. North Branch, MN: specialtypress. 2006: 135-138,202. ISBN 9781580070874.

books.google.com

"Swift Attack Bombers Race For Jobs In Army Air Corps." （页面存档备份，存于互联网档案馆） Popular Mechanics, June 1939.

web.archive.org

"Stearman XA-21 (Streamlined Cockpit)." Museum of the United States Air Force. Retrieved: 17 July 2017.
"Stearman XA-21 (Stepped Cockpit)." Museum of the United States Air Force. Retrieved: 17 July 2017.
"Swift Attack Bombers Race For Jobs In Army Air Corps." （页面存档备份，存于互联网档案馆） Popular Mechanics, June 1939.