Cnp mortar british 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 mortar british 01, BL 15 inch Howitzer
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Cnp mortar british 01, A British howitzer being assembled, A British howitzer being assembled
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ブルドーザー弾
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Cnp 迫撃砲 イギリス製01、組み立て中のイギリスの榴弾砲、イギリスの榴弾砲
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mortar (construction) asserted mortar mortar (weapon) mortar and pestle