Cnp train turret 01.jpg
Originally scanned from: GWS - The Great War: The Standard History of the All Europe Conflict (volume four) edited by H. W. Wilson and J. A. Hammerton (Amalgamated Press, London 1915)

According to http://www.firstworldwar.com/photos/sources.htm, “Each photo is believed to be copyright-expired except where indicated.” The site has been up for seven years and sources for the photos cited so it is reasonable this claim of copyright expired status has stood the test of time.

Note: other than the source of the image and the assertion of copyright free status, detail information such as credits for each photographer and image provider was not indicated for each image.
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Cnp train turret 01, Canon de 19 cm modèle 1870-93
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en
Cnp train turret 01, Canon de 19 cm modèle 1870-93, Canon de 19 cm modèle 1870-93
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Cnp列車砲塔01、19cmモデール砲1870-93
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Cnp列車砲塔 01、19cmモデール砲 1870-93、19cmモデール砲 1870-93
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gun turret asserted turret