Disruption during movement.

[LarkinVB]

Moving units can get disrupted by enemy fire during their move in non phased games. Can someone please point me to the rules page where I can read about this (Campaign Gettysburg). I can't find anything about the probabilities for this to happen.

[krmiller]

Moving units can get disrupted by enemy fire during their move in non phased games. Can someone please point me to the rules page where I can read about this (Campaign Gettysburg). I can't find anything about the probabilities for this to happen.

From User

Morale Section
When a unit suffers casualties due to combat, it will (this should say "may", only time units 'will' make Morale Check is if at Max Fatigue)
take a Morale Check to see if it Routs or becomes Disrupted at the end of the Phase.

When Morale Checks are applicable, they are determined based on a probability using the given loss as:
loss / (loss + 25)
Thus a unit that takes a loss of 25 men has a 50% chance of requiring a morale check and a unit that takes a loss of 100 men has an 80% chance of requiring a morale check.
(this is done after each casualty determination, Fire or Melee.  Firing multiple units at once casualties from each separate unit are added before making this determination)

The resulting Morale value is compared with a random Die Roll from 1 to 6, and if the Die Roll exceeds the Morale value, then the unit fails the Morale Check.

A unit that fails the Morale Check during a Defensive Fire Phase (or during movement for Turn Mode)
becomes Disrupted, while a unit that fails the Morale Check during any other Phase becomes Routed. (at end of phase/turn)

My comments

[Mowgli]

Unfortunately, the manual for the Napoleonic/Civil War battle titles is not very helpfull at all.

As krmiller has wirtten:

If a unit suffers casualties due to enemy opportunity fire, it may need to conduct a morale test. The likelihood depends on a) the size (manpower) of the unit and b) the number of casualties suffered. The smaller the unit and the higher the casualties, the more likely the unit needs to undergo a morale check. If the unit fails the morale check, it becomes disrupted (and immediately loses a third of its movement budget). If it passes, nothing happens.

Tips:
To prevent morale checks from opportunity fire, you may screen your units with other units (units block lines of sight! no line of sight -> no opportunity fire) or with skirmishers (shooting through skirmishers reduces fire effectiveness by 20% (not cumulative)).
To increase your chances to pass the morale check, have a commander stacked with the unit.

[LarkinVB]

Thanks.

"When a unit suffers casualties due to combat, it will take a Morale Check to see if it Routs or becomes Disrupted at the end of the Phase."

It wasn't obvious to me that this is applicable during movement each move step.

[Mowgli]

Thanks.

"When a unit suffers casualties due to combat, it will take a Morale Check to see if it Routs or becomes Disrupted at the end of the Phase."

It wasn't obvious to me that this is applicable during movement each move step.

From my understanding (the manual is not helpfull at all - the most complete manual for this engine is the one that comes with "Renaissance/Pike and Shot"): 

Every time a unit gets hit by enemy opportunity fire (when you move it in your turn), it checks whether it needs to pass a morale test based on the casualties suffered versus its unit size (formula below). The more casualties suffered and the smaller the unit, the more likely it is forced to conduct a morale test. If it does need to undergo a morale test and it fails the test, the unit gets disrupted. If it passes, nothing happens.

If your unit was hit (assaulted, fired upon) in the enemy turn (once or a number of times), it checks whether it needs to pass a morale test at the end of the enemy turn/at the start of your own turn. The formula is the same as above (unit size vs. casualties suffered), but the number of casualties are the accumulated casualties from all enemy actions in the last enemy turn. The effects are more severe: If the unit needs to undergo a morale check, it automatically becomes disrupted. If it fails the morale check, the unit is routed (disrupting nearby units, maybe even routing them too) and immediately conducts a rout-movement. Note that units which have just routed/disrupted at the start of your turn cannot recover in the very same turn.

So basically, there are two types of "shock" tests: 
1) SMALL TEST: triggered IMMEDIATELY by enemy opportunity fire; size vs. casualties; on morale test fail: disrupted, on pass: nothing happens
2) BIG TEST: At the start of your own turn; size vs. accumulated casualties suffered during the last enemy turn; on morale test fail: routed, on pass: disrupted.

NOTE: I think that a unit which has lost an assault initiated by the enemy automatically needs to conduct a morale test at the start of the turn (it skips the casualties vs. size test).

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Shock test formula

casualties suffered* / (   casualties suffered* + unit strength**/10   )

* for big test: accumulated casualties during last enemy turn, for small test: casualties from the opportunity fire action
** this is capped at 250, i.e. units smaller than 250 men still count as having a strength of 250; this mainly helps cavalry and skirmishers

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Interpretation/Implications

From this it is clear why it is incredibly difficult to disrupt attacking units unless they need more than one turn's movement to reach you. Opportunity fire is rather unlikely to cause disruption, because the casualties of a single fire action are small (unlikely to trigger a morale test) and the target's morale is usually good enough.

You can also see that larger units have stronger morale (regardless of their morale value). Because due to the formula above, it's harder to force morale tests on them.

Also, offensive units usually have an advantage. Approaching the enemy or failing an assault cannot rout your unit. By contrast, a successfull assault forces a big morale test on the enemy and may rout him.

This morale system also means that player feedback is delayed, which is rather unintuitive. For example, in Napoleonic battles (same engine), if you charge with your cavalry and push the enemy back (successfull assault), you will only see the true impact of your charge at the start of the opponent's turn, when the game checks whether the charged unit routs (causing disruption to neighbouring units) or stands. So the effects of your actions are always "delayed". I suppose it helps to prevent cheesy igougo tactics/exploits.

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Example:

A squadron of dragoons (120 men, morale B) approaches an enemy infantry bataillon (700 men, morale C, line formation). When the Dragoons enter the range of the batallion's muskets (2 hexes), the batallion opportunity-fires at the Dragoons for 3 casualties (-50% fire power for opportunity fire; long range; bonus for firing at cavalry). The game conducts a small shock test for the Dragoons like so:

3 (casualties) /  (    3 (casualties) + 250 (minimum strength) / 10    )    = 0.107  

So there is only a 10.7% chance that the fire forces a small morale test upon the dragoons. Let's say it does. The dragoons have a morale of B. Let's say that no additional modifiers (leaders, fatigue, etc) apply. So the dragoons have a 83% chance and easily pass their morale test, which means that they're fine (no disorder). If they had failed, they would now be disordered (which would most likely stop the charge, given that disordered units have -66% offensive assault power).

The dragoons continue to close in on the infantry in good order. They're now adjacent to the infantry. This movement randomly fails to trigger opportunity fire.

Now the dragoons declare a charge on the infantry. This randomly triggers the infantry's opportunity fire, which inflicts 10 casualties on the dragoons. There is a chance of 28.5% (10/(10+35)) to force a small morale test upon the dragoons. Let's say the dragoons pass the shock test, so they don't need to test for morale.

Now the charge is resolved. Let's say the dragoons are successfull (push the infantry back), cause 50 casualties on the infantry which is now automatically disrupted. The cavalry suffers 20 casualties and is also disrupted. Note that by this stage, it is impossible for any unit to rout.

Next comes the infantry's player's turn. As the infantry had been pushed back in an assault, it automatically needs to conduct a (big) morale test. The infantry batallion has a morale of C, is disrupted (-1 morale) and - due to the assault - has exceeded the first level of fatigue (-1 morale). So the chance to pass the morale test 1D6 (-2) vs. 4 (morale C), which is 33%. The unit fails and immediately becomes routed. All friendly units in the same and adjacent hexes automatically become disordered (if disordered already: may not recover) and also need to pass a morale test in order not to be routed. 

Let's say that both neighbouring infantry batallions of the assaulted unit stand their ground (pass their morale tests) and are therefore just disordered (not routed). They pivot so that they can fire on the enemy cavalry which has broken into the line. (The pivot also serves to trap the cavalry in zones of control). Unfortunately, the infantry's fire power is now much reduced for being disordered (-50%) and having moved (pivoted; -50%). Nevertheless, thanks to the bonus for firing against cavalry, one unit inflicts 4 casualties, the other unit 7 casualties on the dragoons. 

At the start of the dragoons' player's next turn, the dragoons (79 men remaining) need to conduct a big shock test: They have suffered a total of 11 casualties in the last enemy turn, so the chance for a morale test is: 11 / 11+25 = 0.305, i.e. 30.5%. Let's say the shock test is passed. So the dragoons do not need to conduct a morale test (no chance to become routed) and may even recover from their disruption (depending on their brigadier's command rating this turn). If they had failed the shock test, the dragoons would have stayed disrupted (no chance to recover) and - on a failed morale test (-1 for being disrupted) - may have routed.

SIDENOTE: In this example, a single sqadron of dragoons was used for the assault. I know that it's highly unlikely that a single squadron can win an assault against a large batallion. In a realistic setting, you would be charging with several squadrons stacked together. From my understanding, it is almost impossible for infantry fire to stop such a charge for two reasons: 1) the infantry opportunity fire hits only one of the stacked squadrons, not all of them. 2) opportunity fire cannot rout units (so there is no chance to disrupt all the stacked squadrons). One thing to note though is that every cavalry loss significantly hurts the assault power of cavalry, as a single cavalry trooper has his assault power multiplied by the cavalry charge parameter.

[krmiller]

From my understanding (the manual is not helpfull at all): 

Every time a unit gets hit by enemy opportunity fire (when you move it in your turn), it checks whether it needs to pass a morale test based on the casualties suffered versus its unit size (formula below). The more casualties suffered and the smaller the unit, the more likely it is forced to conduct a morale test. If it does need to undergo a morale test and it fails the test, the unit gets disrupted. If it passes, nothing happens.

.....
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Shock test formula

casualties suffered* / (   casualties suffered* + unit strength**/10   )

* for big test: accumulated casualties during last enemy turn, for small test: casualties from the opportunity fire action
** this is capped at 250, i.e. units smaller than 250 men still count as having a strength of 250; this mainly helps cavalry and skirmishers
.......

It looks as if you are quoting the Napoleonic Users Manual here.
I'm not as familiar with it but I checked and yes those games use unit strength to determine if Morale Check is required.
According to the manuals the ACW games use only casualties caused in the current combat.
loss / (loss + 25)
This check is used whether the combat is Fire or Melee.
According to the ACW Manual the only time a unit is automatically required to check morale is if the
1. Defender in a melee loses the melee and has to retreat.
2.  Unit is at Max Fatigue.

[Mowgli]

You're right. This is a small difference between the ACW and Napoleon games: In ACW, the strength used for shock tests is always 25, whereas in the Napoleon-games, it's "current manpower/10" (capped at at leat 25). I have to say the ACW method (which is similarily also used for the Panzer Campaigns series) makes more sense to me as it doesn't blur the difference between unit size and morale.

Other than that, ACW seems to work like I have described here, with big and small shock tests and big and small morale tests. You can also judge by the command report: "X units routed out of Y units tested". Y tells you, how many units have failed their big shock test and are now at least disrupted. X tells you how many of those units have failed their big morale test and have routed. (The other ones have passed their big morale test and are thus only disrupted)

You're correct that being successfully assaulted leads to an automatic (big) morale test (the shock test is skipped).
Same is probably true for units suffering casualties when at maximum fatigue, but I haven't tested it. I wonder if max. fatgiue makes a unit skip both big and small shock tests.