The mention of a naval mount comes the Schiffer book that was originally published in German and written by Germans too. Here is the picture below. It probably comes from “Der Atlantikwall – Vol II – 1989" from Zimmermann. (So all my sources are German, aren’t they
? Just kidding !). The text attached to the picture is "Left: A 10,5 cm Filed Cannon 331 (f) on a turn-of-the-century naval mount. (Zimmermann)."
But the book does not mention the type of the original mount. However, the mount looks the same as in the casemate at Guernesey.
The armored shield looks like naval origin of turn-of-the-(XXth)-century. It could be why Zimmermann refers to it as a naval mount.
The mount itself also looks very different from a mittlere Sockellafette IV.Emmanuel
?
Anyway, it seems that their designs were based more on turn-of-the-century naval mounts than fortress gun mounts, as 10-15 cm caliber naval guns were widespread around the main navies, unlike fortress guns of these calibers.
