This post is the result of a couple of encounters with one of those weird pieces of ordnance that came out of the late 19th Century. I’m going to post the links in reverse order to which I encountered them, starting with this tumblr post of a small metal pillbox used for anti tank purposes on the Hindenburg Line on the Western Front in WW1
https://en.wikipedia.org/wiki/Hindenburg_Line
. Here’s the post.
Now the author of the blog couldn’t find out much about what the things was, but in the weird sort of coincidences that the internet creates I had actually run into the cupola and it’s ordnance in a completely different setting. The cupola is called a Fahrpanzer and they were designed to be portable emplacements in fortifications.
https://en.wikipedia.org/wiki/Fahrpanzer
I know about the Fahrpanzer because last week or so I encountered this on Pinterest.
The picture came from this wonderful artist on Deviantart who did a series of illustrations for a book in Romania, where most of the Fahrpanzers were sold by the German company that built them, for various fortifications.
http://wingsofwrath.deviantart.com/gallery/54089835/Nonfiction
During WW1 the Fahrpanzers in Romania were more or less obsolete, pointing in the wrong direction(toward the Russians), dismantled for their guns and lost in the turmoil of WW1 and I just saved the picture in my ordnance folder assuming that the Fahrpanzer was just another one of those obscure pieces of European ordnance that was good for curiosity purposes, but not much else. Then I saw the post above where at least two(the picture in tumble post show two different Fahrpanzers if you look at them closely, one is missing the builders plate on the back), and probably a lot more were emplaced on the Hindenburg Line as antitank guns, a role that they are actually well suited for as long as the armor of the tank is not very thick, which all the armor on all the tanks of WW1 was.
Here’s a stack of Fahrpanzer links.
First of all, the technical drawings from the Copenhagen military museum who apparently have the only 37mm Fahrpanzer.
http://www.vestvolden.info/Skytset.htm
Click to access Taarnet.pdf
Click to access Taarn_indvendig.pdf
Click to access Taarn_detaljer.pdf
Click to access Ammunition.pdf
The Bulgarian Military museum has a 53mm(or 57?) Fahrpanzer
http://www.bulgarianartillery.it/bulgarian%20artillery%201/Gruson%2057mm%201892.htm
http://www.bulgarianartillery.it/bulgarian%20artillery%201/Gruson%2057mm%201892_Sofia&Athens.htm
The Athens military museum has two apparently
http://www.fort.mariwoj.pl/p002gruson.htm
Some pics I found on google.
http://s1039.photobucket.com/user/Bencejas1/media/Dunker-Church-Truce_zps9zuqepf6.jpg.html
http://s1039.photobucket.com/user/Bencejas1/media/DSCF1092_zpshfsd3jq1.jpg.html
http://s1039.photobucket.com/user/Bencejas1/media/2011_0529_un_peacekeeper_zps3grylxr3.jpg.html
http://s1039.photobucket.com/user/Bencejas1/media/66305428bc1c013bfe381961dabf168d_zpstdy7fpzv.jpg.html
Some Fahrpanzers in deployment.

In a war that already the favored the defensive, the Fahrpanzer would actually be a nasty piece of ordnance even if the gun was obsolete. It the black powder gun was replaced by a more moderns weapon, the fact that these things could be brought up, dug in and once emplaced, almost impossible to hit with the direct fire weapons of WW1 tanks and requiring a direct hit from over head by a howitzer or mortar. Now that I see them I’m not surprised that the Germans, short on both resources and men in 1917 pressed these things into service. Which almost certainly made the Tommy’s, Doughboy’s and Frenchy’s jobs just that much harder. Such was WW1.