Depth of reconnaissance

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There was a rule of thumb for the necessary depth of reconnaissance in the horse age. I think it was that the scouting cavalry was supposed to be three main army day's marches ahead.
I'm not sure on the exact number and it has lost relevance long ago anyway. The driving factor back then was the delay in messaging (couriers had to ride back and would at times spend much time searching for the army HQ).

There were rules of thumb later as well, but the use of such rules of thumb would lead to impossible recce depth requirements if speed of movement was used as a variable.

We need something different today. Today's armies have been freed from many shortcomings (slow communication, slow movement) that plagued armies before the 20th century and we need a new reasoning about recce depth requirements.

My best guess candidate would be our reaction lag multiplied with the velocity of enemy attacks and multiplied with a constant:

required reconnaissance depth =
reaction lag * enemy attack speed * constant

The constant is at least =1, preferably greater to account for friction.
The reaction lag is a bit fuzzy; it depends on the ambition. A very ambitious definition would be the time lag from recce units learning about something till main body HQ having changed its intent AND re-positioned and prepared the units under its control accordingly.

No matter what kind of level we're talking about - battalion, brigade or corps - such a rule of thumb should be useful.

It means that no matter how the enemy wants to hit us to his advantage, we would have enough time to parry or evade IF our recce succeeds in its mission at the required depth (distance ahead).

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This easy (astonishingly, math is at times really making things easier) formula leads to several noteworthy conclusions:

(1) The necessary depth of our recce depends on our unit agility on the battlefield. More agile units need less reconnaissance depth/advance.

(2) An enemy who's very rapid in his execution of offensive actions in turn increases the need for reconnaissance depth.

(3) Becoming more rapid on the offence would increase the enemy's reconnaissance requirement and we may become too quick for him (if we weren't yet).

(4) There's a blind area in which reconnaissance has limited or no utility for early warning.
It's therefore preferable to keep a greater distance to the enemy than the required reconnaissance depth unless we're ready for the fight. This requires something that keeps him at a distance, of course.

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The old reconnaissance challenge does still exist (and reconnaissance units have much more utility than just early warning).

The idea that aerial reconnaissance could and would be reliable and satisfactory has been postponed again and again. We still need reconnaissance up close, able to interrogate prisoners and interview civilians. Recce troops who can identify tracks up close, search evacuated resting places for hints, inspect a bridge from below for explosives, go into buildings and look behind camouflage nets that conceal dummies.

The question of the necessary reconnaissance depth is a very important one. It influences the optimal force structure and design. Greater depth requires more recce units, greater recce vehicle endurance, longer range communications and greater survivability of recce units against aerial threats.

S O

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