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PHOTO INTELLIGENCE FOR GROUND FORCES 3 
Detection of personnel is self-limiting in that time is not wasted on unprofit- 
able targets; they are invisible unless in good concentration. The interpreter 
looks for the effect that concentrations of personnel have on their environment, 
much as a physicist looks at a meson track on a photographic plate and, without 
ever having seen the meson itself, knows with absolute certainty that it has 
been there. At the same time, there are few important aspects of tactical photo 
interpretation which require a greater general intelligence sense. 
Now the significance of these items of prime tactical photo interest is not 
limited to their own undoubted importance. Consider them from the viewpoint 
of the end users of the intelligence. If some of today’s photographs bear the 
particular little dots that may mean mortars or machine guns or mines, it will 
help tonight’s patrol not at all to learn about them tomorrow. And what of the 
anti-tank guns also newly visible? A tank raid kicks off in two hours. The cry 
is constant and unvarying, "we want to know now." 
As a matter of routine, the tactical interpreter works with his customers 
sometimes literally hanging over his shoulder. There is always a deadline for 
warning one element or another and the interpreter regularly operates under 
the nagging pressure of a host of blobs and dots, all clamoring for attention by 
the same deadline. In the tactical situation moreover, the interpreter has a 
personal interest in his speed and thoroughness. It is entirely possible that a 
gun he does not find at four in the afternoon will blow him into the sky, trusty 
stereoscope and all, at nine in the evening. 
The word which characterizes photographic counterbattery intelligence 
is "urgent." The guns which are particularly referred for photographic search 
are the ones that hurt most. They hurt most because they are not found easily 
or at all by other means. They are not found by other means because very often 
these guns have several prepared positions which they occupy in rapid rotation. 
These factors call for the utmost rapidity in discovery and report. 
So if the interpreter is given a sortie on Monday, he must interpret it com- 
pletely on Monday because the gun he finds on it on Tuesday has very likely 
either killed his friends or moved away. It is a fleeting target. Even on Monday, 
in fact, the signs of unusual personnel activity the interpreter finds may only 
be the evidences of the previous night's concentration and attack. He maneuvers 
around this by keeping a running file, available for instant targetting, of those 
places where men could advantageously and safely accumulate. But this 
strategem is itself a tribute to time. 
The interpreter who is acquiring tactical experience learns quickly that his 
activities must be attuned to an urgent tempo, that is part of the technique. 
He works in tremendous spurts which are triggered by the arrival of each fresh 
sortie. He never has time for the studied subtleties of the grand plan or masterly 
revelations. 
There is then an inescapable fact: the mistress of tactical photo intelligence 
is speed. 
II 
If a little thought is given to what the tactical interpreter does, tactical needs 
in other words, and how he does it, it can be seen that certain conditions would 
enhance effective operations. The principles developed here are controversial ; 
some interpreters are opposed. Surprising unanimity exists however, among 
those interpreters who have actually worked in a tactical situation. These 
conditions, or principles or requirements fall into these general categories: 
1. Limitations related to the speed with which intelligence can be derived from 
photographs and still be tactically useful.