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The conceptual difference between a force suitable for holding (and slowly moving) a frontline and a force suitable for rapid exploitation of the absence of an uninterrupted frontline (including pursuit) is stark.
It takes different tactics, different organisations, notably different hardware, different tactical mindsets and different logistics to become really good at either, and it seems to make no sense for an army to try to build formations that are good at both, for that appears to be very inefficient.
The line formation
A line formation would follow the heritage of an infantry division of WW2 (not the Western Allies 1944/45 kind). It creates an elastic defence-in-depth with multiple prepared positions. The field fortifications should be well-hidden, have overlapping fields of fire, use the parapet defence concept and use overhead cover against 152 mm HE shells exploding a few metres above (with proximity fusing) or a 82 mm HE mortar bomb scoring a direct hit.
The general concept is to avoid that opposing forces detect the platoon positions, so they need to be well-hidden, radio emissions need to be avoided (and faked in false positions) if possible and fire team-sized pickets need to be in front of platoon positions. Attackers should be delayed by the pickets, endure indirect fires until they make surprise contact with hitherto unknown main defensive positions. The surprise effect is then lost, and defenders may move to other, still hidden, positions for renewed defence with new pickets. To remain in known positions would lead to avoidable casualties to hostile indirect fires.
Some
platoon positions would double as points for launching quick
counter-attacks. All intrusions of opposing forces into a platoon
position would trigger a counterattack by a rear platoon, a company in
trouble would spring a counterattack by another company, a battalion in
trouble would spring a counterattack by another battalion. These
counterattacks should be self-evident and near-instant, but use unpredictable routes
& directions. Counterattacks are not necessary when the hostile attackers don't succeed at breaking into main defensive positions, though.
Lost terrain may later be retaken with deliberate attacks with limited objectives. Sometimes the lost terrain will even be abandoned by frustrated hostiles if their position there becomes untenable.
The typical movement under pressure would thus be retrograde. Positions should be capable of 360° defence, but optimised for about 120...180°. Leaders will be very concerned about securing flanks, staying in communication with neighbouring friendlies, avoiding friendly fires.
Casualties would be inflicted by 90+% through indirect fires (mortars, artillery), nowadays maybe including drone attacks.
Attacks would make generous use of artillery fires. An attacking company might receive support from the majority of artillery of a division-sized force. Well-executed artillery fires would use suppressive fires and smoke to keep some hostiles from defending effectively. The defenders in the path or on the objective would be subjected to neutralising artillery fires at least. They may not die or be wounded, but almost all of them should be combat-ineffective for psychological reasons. The attackers should further scare the defenders (noises, tanks) and give them opportunity to surrender (megaphones, attacking infantry intent and able to accept surrenders).
Attacks would typically be frontal, though advance into one objective may enable a flank attack on another objective.
Many tricks of the trade can be exploited in such deliberate attacks. The best possible attack does thoroughly discourage local resistance. This is about tactical psychology on the levels up to battalion command. It's much better to see hostiles running or to accept their surrender than to shoot it out.
Forces of the line will face near-continuous attrition and require influx and integration
of many replacements. Replacements other than officers should be
integrated in reconstitution periods at a rather safe distance from the
frontline (certainly more than 40 km). NCO and enlisted replacements
should not trickle directly to units at the frontline.
Such forces don't need very many armoured vehicles. A few dozen tracked APCs could suffice for an entire division of the line, but a battalion of tanks would be welcome support. Repeat; "support".
The exploitation formation
It would then move quickly to exploit the breakthrough. Maybe it's tasked to reach an objective such as a geographic bottleneck (maybe a bridge or a pass) or an obstacle (coast, swamps, mountains). Maybe it's tasked to link up to another spearheading force to complete a two-pronged encirclement. Maybe it's tasked to roll up the frontline by moving parallel to it, overrunning support units. Maybe it's tasked to reach and overrun an airfield, high-level headquarter or a depot/railhead area.
Exploitation formations such as tank brigades (should) have different mindsets than line formations such as an infantry division. Their leaders' thoughts are focused on the next (interim) objective whenever they have reached an (interim) objective), and they would prefer to either evade hostile counterattack forces or to deal with them with an aggressive attack of their own. Line formations would often have their (small) units prepare for defensive actions on the position once they have reached a (usually less ambitious) objective.
Forces of exploitation benefit greatly from off-road mobility for a great choice of routes, from long driving range of vehicles, from carrying supplies for several days of operations and from bulletproofing of all vehicles (the latter due to sketchy all-round security). They will move among hostiles, need a 360° security effort during rests and the ability to project support fires 360°, but they do rarely face battle-ready combat troops, manned field fortifications or minefields during exploitation.
Their mentality needs to be very different. Quickness of movements, rapid reactions and total acceptance of unsecured flanks and rear become essential. The burden on the human mind and body won't be sustained for more than about four or five days before a dangerous drop of performance. Longer-lasting actions need thus be much less intense than actions of up to four days.
These exploitation formations have great use for reconnaissance, which still includes scouting on the ground even if there's support by bird's view sensors. Scouts on the ground can draw fire from hostiles who eluded our sensors.
To loan an analogy used by a WW2 veteran officer from memory; they [German WW2 tank divisions] resemble more a nimble rapier than a sturdy broadsword. You need to know where to thrust and must not rely on brute force, or else such forces will be worn down quickly.
The line of sight combat of such exploitation formations is a nimble switching between tanks leading on open terrain and dismounted infantry leading on close terrain. The optimum ratio between tank and infantry battalions in such mobile forces is 1:1 (according to WW2 experiences, taking into account WW2-ish personnel strengths of infantry battalions).
These forces should strive to maximise the count of prisoners made rather than to maximise killing. The handling of prisoners of war is a challenge, though. Sometimes captured enlisted personnel would better be disarmed and locked into rooms with some drinking water rather than be guarded and taken along.*
Such mobile warfare consumes much more fuel than munitions. The vehicle and the logistical components of a formation meant for exploitation should be oriented accordingly.
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Most armies are traditionally incapable of getting the exploitation formations really right. They try and are proud of their achievements, but simply never achieved the rapidity and nimbleness achieved in some other armies. A lack of rapidity exposes exploitation formations to counterattacks (remember the unsecured flanks and rear) and often foregoes an element of surprise and many opportunities.
Forces of the line are much less demanding, albeit there are huge differences in how sturdy they really are when tested for real. Line formations are much cheaper in terms of equipment, much cheaper in terms of training expenses (both duration of training and cost per training day) and much better-suited to reservist forces. Exploitation formations absolutely need real exercises in the field; computer and tabletop exercises don't come close to suffice as simulations of actual mobile warfare. The exercises also occasionally need to span at least four days across larger areas than any army training ground in Europe has to offer.
NATO armies attempted to create mechanised brigades and divisions capable of doing both, and in the process few armies achieved great rapidity and nimbleness for exploitation and those formations lack infantry for a sturdy defence-in-depth on a wide frontage. Light forces (airborne, mountain, European marines, rangers) aren't good at either role** and would at best supplement actual forces of the line in specific terrains (mountains, swamps, woodland, towns and cities). I am unconvinced that forces with wheeled bulletproof vehicles would be suitable for the exploitation role, though this depends on how very much not battle-ready the opposition is in the area (and on how soft the ground is).
S O
*: Back in 1941 many captured enlisted Red Army soldiers were disarmed and merely told to walk towards some prisoner collection point, as advancing Panzerdivisionen lacked the infantry strength to take care of them.
**: Not enough organic indirect fire capability to stand & fight as a line formation on their own.
P.S.: A third kind of formation is notable and suitable for warfare without frontlines: A skirmishing and screening force. Such a force would substitute for a much higher force density effort with formations of the line forming a defended front-line. Some NATO forces have had such formations, either under the guise of armoured reconnaissance or as 'cavalry' screening force with mostly a delaying action mission. I thought and wrote much about such skirmishing & screening forces in past years, but the demonstration of defended front-lines in Ukraine indicates that we should rather look at the forces of the line. A land war between Russia and PR China is a scenario in which Russia could make good use of skirmishing & screening forces, but it would likely lack the competence to pull them off.
I did illustrate this to make it easier on the eyes. The first symbol is a friendly infantry division, the 2nd one a friendly tank brigade. WW2 experience was that it was fine to organise forces of the line in divisions, but exploitation formations should be more nimble than a tank division. A tank division commander usually only had direct control over a regimental-sized vanguard anyway. The optimum during WW2 was a tank corps consisting of at minimum three small tank divisions. The battalions would be 50% square tank battalions and 50% triangular infantry battalions (on APCs), with self-propelled organic divisional artillery. You needed a tank corps for spearhead operations because a tank division on its own could not penetrate deep and handle the flank counterattack risk at the same time.
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