During the Coalition Invasion Arc, one of the highlights included Shouheikun's manipulation of the battlefield using the Echelon Assault for Mou Bu's army against the 3rd army of the Chu.

As we gathered from the developments following Mou Bu's enforcement of the formation, the objectives were as follows:

1. Primary: Take out Chu Commander-in-Chief — the Sword of the Coalition Army — Kan Mei (offense/indirect maneuver)
2. Secondary: Weaken Chu forces while carving out a path for Mou Bu to advance towards Kan Mei (feint-defense/direct maneuver)

That said, we shall briefly go over the formation used and discuss how, despite its impracticalities, did it succeed under the army of Mou Bu against the Chu.

The First Wave of the Echelon Assault - Chapter 295, \"A New Form\"

The Echelon Assault Theory (as explained by Mou Ten):

When a line formation such as that is hit by an "Echelon Assault", a shockwave is transmitted diagonally through their ranks.

Those who are hit will be pushed back three steps diagonally and the next man, two steps. Those who are hit by both will move back four steps. These movements will pass through the enemy ranks like a wave, causing small disruptions to the troop formations.

However, even a small disruption like that is enough to disturb the enemy soldier's cohension. And [at that] exact moment, your charge hits the enemy from head on. Thereby once again creating the next shockwave to pass on.

So long as this shockwave is able to pass on through the enemy line without interruption and the attacks are able to follow in succession, then an "Echelon Assault" will be extremely effective.

Criticisms:

"At the end of the day, this stratagem was considered too impractical for actual use — since keeping the shockwave going without halt is far too difficult." (Mou Ten)

"Part of this can be due to the timing of each unit hitting the opposite force. Too soon and the force wouldn't travel through the opposing force properly, but too late and the enemy would have time to adjust their forces accordingly." (Assault Echelon Formation)

"...Mou Bu's army has sent [...] half of their total number [... so] all that's left is to throughly squash the enemies that have thrown themselves right into our arms." (Kan Mei on the first wave of the assault)

"...splitting his bulk into two separate directions and so far apart from one another, there would be no going back in the event of failure." (Jin Ou on the second wave of the assault)

As deduced by Chu's strategists, Qin most likely employed this maneuver due to the Chu army's formation as well as the landscape of the battlefield — something Kan Mei army strategists Bei Man and Jin Ou pointed out:

"It would appear the large size of our army has instead backfired on us."

"Due to these narrow plains, we had no choice but to deploy our troops in a tighter formation. Thanks to that, the wave is able to travel through the formation easily."

Given that, the Chu Army hurriedly sent out 5000 reinforcements to hit Qin's right flank — which will most likely contain Qin's strongest units — in order to disable the assault from reaching Kan Mei's HQ.

Following this, Mou Bu then launched another wave of the same formation to scatter Chu's forces — who then sent out 10,000 men to counter.

The Second Wave of the Echelon Assault - Chapter 309, \"The Path to Kan Mei\"

In summary, the 40,000 strong Mou Bu Army was thus employed in the following maneuvers:

• 20,000 for the first wave of the Echelon Assault to charge against the Chu's 60,000 men (as a diversion)
• 15,000 for the second wave to weaken the wings of the Chu's army (another diversion)
• 5,000 for the main attack towards Kan Mei's HQ containing 10,000 men

How unfortunate then that the Chu underestimated Mou Bu's maneuver solely because they looked down on his strength and uncharacteristic use of tactics — something that Shouheikun most likely counted on in order for Mou Bu to:

"...take the head of Chu Commander Kan Mei, the symbol of the Coalition Army's might!"

Rather than dismiss Mou Bu, though, the Chu should have realised that Mou Bu choosing to depart from his usual shtick was a step towards the fall of Kan Mei.

"Here lies the important part. The weakness of the line abreast formation lies in the two edges.

By sending out those two waves, the enemy will without doubt assume that your aim is to collapse their two flanks, and will react by diverting the majority of their troops far away to the two edges.

This operation is the only shot we have for you to take out Kan Mei who is hiding in the back. And even then, the best it can do is open up a path for you.

The rest is all up to you, Mou Bu. [...] Failure is not allowed." (Shouheikun)

The step that led to the collapse of the whole coalition.

All in all, it was a strategy that perfectly illustrated the following principles from Sun Tzu's Art of War:

• The natural formation of the country is the soldier's best ally.
• To ensure that your whole host may withstand the brunt of the enemy's attack and remain unshaken — this is effected by maneuvers direct and indirect.
• If we wish to fight, the enemy can be forced to an engagement even though he be sheltered behind a high rampart and a deep pitch. All we need do is attack some other place that he will be obliged to relieve.
• If his forces are united, separate them. [...] For should the enemy strengthen his van, he will weaken his rear; should he strengthen his rear, he will weaken his van; should he strengthen his left, he will weaken his right; should he strengthen his right, he will weaken his left. If he sends reinforcements everywhere, he will everywhere be weak.
• Hence the saying: If you know the enemy and know yourself, your victory will not stand in doubt.

Thus said, despite the impracticality of the Echelon Assault, Mou Bu's army succeeded precisely because of their sheer strength — the one facet that Chu kept downplaying to their utter ruin.

I gather that despite Mou Bu's initial hesitation to go along with Shouheikun's plan, he eventually realised that the formation can only succeed with his army as it would allow them to display their full strength — thereby showcasing their might in offensive-oriented battlefronts.

(I surmise that Shouheikun could only entrust this high-level tactic to Mou Bu for this exact reason as well.)

Another thing — I wager that despite Mou Bu's aversion for "cheap little tricks on the battlefield", it does not mean that he automatically dismisses tactics totally, as shown in this arc. Rather, I wager that he understands it really well (or else he would not have been able to execute the timing of the formation perfectly), but prefers not to use it — if only to prove the point that might can outlast tact in battlefields.

That said, the cooperation between Mou Bu and Shouheikun in the execution of this formation allowed the odds to turn in favour of Qin against the Coalition Army.