I don't have my reference books with me right now, but I recognized the model of the howitzer they were using.
Hardly any WW1 RR guns still exist, but a few
WW2 ones still do...
Dahlgren Naval testing center had a 12" RR mount there, and the Washington Navy yard has a 16" mount at their museum...
There are a couple of K5
German guns at the Army Ordnance Museum at Fort Lee (which was at Aberdeen, MD for decades) and at the Batterie Todt Museum at Audinghen, France
When I was stationed at Aberdeen Proving Ground, we used to run PT formations out to one of them as a turnaround point. I never got tired of that.