Apologies if this has been posted before but here's an HD video transfer of archive footage of US Army forces with a pair of captured Big Berthas at the end of the Great War. It's on the Critical Past label and thus is watermarked, but the watermark is not as obtrusive as one might fear. Un-watermarked video can be ordered from them but I imagine it's pricey... The aspect ratio as presented on YouTube is wrong - your best bet is to download the video and view it in VLC with the aspect ratio set to 4:3. I've added a couple of screengrabs from VLC below.
