https://justacarguy.blogspot.com/2018/03/ww1-german-mastfernrohr-persiscope-used.html?m=0
Just A Car Guy: WW1 German Mastfernrohr (persiscope) used instead of tethered observation...
While other participants in the fighting invented various towers to raise a man above with binoculars - the Germans strained their heads...
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