These engravings are illustrations from a 19th Century reference book Aide M moire d artillerie navale The various individual engravings reproduced in Neptunia were obtained from copies of the Aide M moire in personnal collections or from the SHD Marine the Historical services of the National Navy but I do not think that this is very relevant You can find various editions of these books from Gallica or Google books Most other images in this series are from the same source exceptions are the 24 cm guns model 1864 and 1879 Compilation du Commandant de Balincourt the mountings of the 80 pounder howitzer and the open turrent of Suffren M morial de l artillerie navale and the gun turrent of Cerb re Cours de Construction navale