In Panzer Battles Maj. Gen. F.W. von Mellenthin gives his first impressions of Russian tactics, starting with their artful use of infiltration:
Practically every Russian attack was preceded by large-scale infiltrations, by an “oozing through” of small units and individual men. In this kind of warfare the Russians have not yet found their masters. However much the outlying areas were kept under observation, the Russian was suddenly there, in the very midst of our own positions, and nobody had seen him come, nor did anybody know whence he had come. In the least likely places, where the going was incredibly difficult, there he was, dug in and all, and in considerable strength.
True, it was not difficult for individual men to seep through, considering the our lines were but thinly manned and strong-points few and far between. An average divisional sector was usually more than twelve miles broad. But the amazing fact was that in spite of everybody being alert and wide awake during the whole night, the next morning entire Russian units were sure to be found far behind our front line, complete with equipment and ammunition, and well dug in. These infiltrations were carried out with incredible skill, almost noiselessly, and without a shot being fired. Such infiltration tactics were employed by the Russians in hundreds of cases, bringing them considerable successes.
There is only one remedy against them: strongly manned lines, well organized in depth and continuously patrolled by men wide awake and alert, and — most important of all — sufficient local reserves ready at a moment’s notice to go into action and throw the intruders out.
This was only deemed possible by US military analysts because the German army was so spread out over such a large front.
To their peril, I believe. If we’d ever gone to war with the Russians, I think we’d have been shocked at how porous even tight lines can be. I think we learned that hard lesson in Vietnam, where infiltration was so pervasive that there really were no lines to speak of during the entire war. If I’m more than 20 yards from somebody, I can sneak past them without them finding me nine times out of ten. Can any military commander really assume that he can close his front to gaps no larger than 20 yards?
I suppose the US military analysts saw the eastern front, with its vast open spaces, playing out differently from the densely populated western front, as in the previous war.