A Question on Rain and Retreating Armies

[Warren Abox]

So let's say you've just fought a battle between blackpowder armies.  Somewhere around the late 1700s in a generic European theater.  The battle results in a decisive victory for one side, and the losers are going to be hard pressed to keep their retreat from becoming a full rout.  The day after the battle dawns cloudy and wet and miserably rainy.

Does this favor the army trying to get away?  Or does it favor the army who is pursuing the retreating forces?

This isn't a hypothetical.  I'm running through a campaign and it has reached a critical juncture.  If the rain favors the victors, they may be able to wipe out an opposing army.  I already know which army has the advantage in light cavalry, and what the general terrain looks like.  What other sorts of factors should I apply when it comes time to designate losses during the retreat?

Thanks in advance for the help, guys.

[RichBliss]

My first thought is that it favors the losers due to reduced visibility.  If it hasn’t been raining for several days, the roads shouldn’t be impassable and wet gunpowder won’t matter if you are withdrawing

[Emir of Askaristan]

The weather slows down and affects both. If the victor is able to remain in contact it should be because they have enough cavalry or possibly light troops such as Croats etc to harry the loser.

If the loser was routed from the field then their retreat might be faster because order has gone, the weather would magnify their defeat as more order would be lost and numbers of stragglers greater.

If they retreated in good order then movement would be slower due to the weather but without wounded and with less baggage and equipment then they'd have a head start which the weather would maintain, if the armies were otherwise roughly the same composition and moving at the same speed.

[Harry Faversham]

Reading a few accounts of the Allied retreat from Quatra Bras might give you a few pointers? The British legging it, the French after 'em with plenty of Horse, being led at one point by their little man in the funny 'at in person!
Most of the action taking place during a thunderstorm.

[AKULA]

What other sorts of factors should I apply when it comes time to designate losses during the retreat?

Also worth considering the quality of the roads.

Heavy rain could easily turn poor quality roads into a quagmire, and make it more likely that the retreating army is forced to abandon its artillery train (apart from light horse artillery), ammunition wagons, wounded, and maybe even its pay wagons.

[valleyboy]

Does it rain enough to have an effect of the ability to cross rivers, do pursuers risk getting cut off by swollen rivers?
What does it do to fords and bridges, less crossing points, more easily defended by the rearguard?

[Wellington]

I have only an example from the Dark Ages. It seems that after the Battle of Lechfeld in 955 a heavy thunderstorm crossed Bavaria (and belive me this storms can be very bad in Bavaria) and due to flooding and ambushes at the few usable crossing more Magyars drowned than killed in the inital battle.

I assume such thing could happen in Napoleonic times too.

[has.been]

I believe that after Gettysburg Lee managed to outdistance the
Union forces. Lincoln asked his commanders, 'Why?'
They said that the rain was slowing down the pursuit.
He then asked, 'Isn't it raining on the Confederates?'

As said earlier

and wet gunpowder won’t matter if you are withdrawing

, whereas the pursuer would want dry powder
to shoot with. Pursuers, having survived the battle, might be less
inclined to risk their necks during the chase, settling for the less
dangerous prizes of abandoned wagons & equipment.
 

[vtsaogames]

During the retreat from Quatre Bras, rain tended to restrict movemnet to the roads as fields became muddy. I think this aided the retreating Allies.
Barring a flooded obstacle across the path of the beaten army, I should think a cloudburst would aid them. It would also shield any unit(s) that were planning rearguard action.

[jon_1066]

If the army has enough formed units to stand rear guard to delay pursuing cavalry then it will aid the cavalry since the infantry will be hard pressed with muskets unable to fire

But...if it turns the fields to mud then pursuing cavalry will find it harder to outflank rearguards.

As said before it makes it more likely to lose the baggage and artillery if the roads turn to mud.  A sudden downpour may not have much effect but sustained rain might.

As with many things I would simply let the dice decide.  Whatever your mechanic is for pursuit then roll the dice.  If half the army give up and they lose all their artillery the rain favoured the pursuer somehow (perhaps a river couldn't be crossed or a bridge was swept away with half the army yet to cross).  If they get away scot free then the rain favoured the retreating army.  Perhaps that bridge was blown after the retreating army crossed and the ford upstream became impassable.

[Patrice]

If it hasn’t been raining for several days, the roads shouldn’t be impassable and wet gunpowder won’t matter if you are withdrawing

This. If the rain has just begun, it takes some days for the ground to be really wet. And if there has been rain for days, the ground will not dry in a few hours of sun.

However, streams in the bottom of valleys, and fords, etc. can quickly become very difficult or impossible to cross because of heavy rain.

'Isn't it raining on the Confederates?'

I had a cat who, when it was raining too hard in front of the house, believed that it was necessary to go at the back door and check if the weather was fine behind the house. 

[SteveBurt]

This. If the rain has just begun, it takes some days for the ground to be really wet. And if there has been rain for days, the ground will not dry in a few hours of sun.

However, streams in the bottom of valleys, and fords, etc. can quickly become very difficult or impossible to cross because of heavy rain.

I had a cat who, when it was raining too hard in front of the house, believed that it was necessary to go at the back door and check if the weather was fine behind the house. 

Most cats do this, I find. I think mainly because they like getting humans to do things for them. Why do things yourself when you have staff?

[John Boadle]

Imho the situation would favour neither side to any great extent, *on balance*. Reduced visibility and possible poor roads will hamper movement and control for both sides, and add to the sum total of misery all round. Several people have already posted particular circumstances that could favour either the pursuers or the pursued. If I absolutely had to choose I would say the effectiveness of pursuit is more likely to be reduced. During this period, it was hard to get armies to mount an effective pursuit at the best of times, and bad weather exacerbated this tendency. The natural instinct once victory became clear was to collapse on the spot, physically exhausted and morally drained, lick one's wounds, look for food and shelter, try to take stock, call the rolls, re-organise, fill command vacancies, etc. Collecting and caring for the wounded was pretty lethargic by later standards. Some individuals would wander off to seek out missing comrades (not least because they could not rely on their army's medical services to do so), and this caused further disorganisation. Everyone thought they'd done their duty for the time being. Napoleon realised better than most how an energetic pursuit could multiply the benefit of a battlefield victory (eg after Iena in 1806), but mostly didn't manage it in practice.

[vtsaogames]

Effective pursuit is largely a function of how many fresh troops the winner has. Napoleon's greatest pursuit was after Jena. Some 40,000+ French defeated a like number of Prussians and another 40,000+ fresh French troops arrived as the Prussians gave way.

The pursuit after Waterloo was mostly by comparatively fresh Prussians of the I and II Corps. It should be noted they didn't take any eagles.

On the other hand, the Austrian defeat at Marengo resulted when their tired pursuit collided with fresh French troops who arrived after Bonaparte was in general retreat.

[Warren Abox]

You guys are something else.  My favorite parts are when you confirm what I thought I already knew...*ahem* ...but there's a lot of great info in this thread and best of all, some excuses to go chase down more info from historical sources.

Thanks for all your comments, gang.  It's much appreciated.