: These engravings are illustrations from a 19th Century reference book, Aide-Mémoire d'artillerie navale. The various individual engravings reproduced in Neptunia were obtained from copies of the Aide-Mémoire 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 24cm guns model 1864 and 1879 (Compilation du Commandant de Balincourt), the mountings of the 80-pounder howitzer and the open turrent of Suffren (Mémorial de l'artillerie navale) and the gun turrent of Cerbère (Cours de Construction navale),