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I have been playing under the impression that major rivers prevented corps/army from MTSGing in support of another unit. In previous games, on three separate occasions I've had a corps/army on one side of a major river and another corps on the other bank that didn't MTSG. I'd pretty much taken it as a given that corps on opposite sides of a major river didn't provide mutual support. But I just had an occasion in a current game where a corps MTSG'd to an army stack that came under attack despite being on the other side of a major river.

In this occasion, there was a rail line that connected both regions. But that was true once in the past as well. And on two occasions I checked to see how long it would take for either stack to march to the other and the weather was clear with no mud or anything else to slow down movement. So how exactly does a major river influence a corps chances to MTSG? Did I just get unlucky in the past or did I get lucky this time around?

FightingBuckeye wrote:I have been playing under the impression that major rivers prevented corps/army from MTSGing in support of another unit. In previous games, on three separate occasions I've had a corps/army on one side of a major river and another corps on the other bank that didn't MTSG. I'd pretty much taken it as a given that corps on opposite sides of a major river didn't provide mutual support. But I just had an occasion in a current game where a corps MTSG'd to an army stack that came under attack despite being on the other side of a major river.

In this occasion, there was a rail line that connected both regions. But that was true once in the past as well. And on two occasions I checked to see how long it would take for either stack to march to the other and the weather was clear with no mud or anything else to slow down movement. So how exactly does a major river influence a corps chances to MTSG? Did I just get unlucky in the past or did I get lucky this time around?

I think there is a roll to be taken there. But actually you probably don't want it to happen, because major rivers are a major source of disaster where you can end up with a defeated troops unable to retreat/rout and being destroyed. It happens very often to the Union AI attacking Frederiksburg. Ideally you want to avoid that MTSG, because you never know what catastrophy could ensue.

I'm sure there's a roll.

There's always a calculation involved before an MTSG happens. I know things like strat ratings, weather, time to get to the battlefield, and a couple other things can impact whether your unit MTSG's or not. I was just really surprised to see a corps on the north bank of a major river involved in a battle on the south bank of said river! It might've surprised my opponent as well. And it was a solid win this time around, but I hear you on possible disasters! Part of why I'm asking is so I can take this kind of stuff into account in the future.

FightingBuckeye wrote:I'm sure there's a roll.

There's always a calculation involved before an MTSG happens. I know things like strat ratings, weather, time to get to the battlefield, and a couple other things can impact whether your unit MTSG's or not. I was just really surprised to see a corps on the north bank of a major river involved in a battle on the south bank of said river! It might've surprised my opponent as well. And it was a solid win this time around, but I hear you on possible disasters! Part of why I'm asking is so I can take this kind of stuff into account in the future.

It has happened to me before and ended very poorly a couple of times, so for example as the CSA i always try to get a 3 star to command an army in western tennesse and one in central tennesse to avoid and MTSG over the Tennessee river. by roll I meant that there might be an extra roll or negative modifier when trying to MTSG over a major river.

The detrimental factor of having to cross a river to successfully MTSG is the extra time it takes the MTSG'ing force to cross the river.

Here's the Wiki description:

http://www.ageod.net/agewiki/Combat_Explained#Marching_to_the_sound_of_the_guns

FightingBuckeye wrote:I have been playing under the impression that major rivers prevented corps/army from MTSGing in support of another unit. In previous games, on three separate occasions I've had a corps/army on one side of a major river and another corps on the other bank that didn't MTSG. I'd pretty much taken it as a given that corps on opposite sides of a major river didn't provide mutual support. But I just had an occasion in a current game where a corps MTSG'd to an army stack that came under attack despite being on the other side of a major river.

In this occasion, there was a rail line that connected both regions. But that was true once in the past as well. And on two occasions I checked to see how long it would take for either stack to march to the other and the weather was clear with no mud or anything else to slow down movement. So how exactly does a major river influence a corps chances to MTSG? Did I just get unlucky in the past or did I get lucky this time around?

key is the criteria for MTSG:

resBaseChanceDef = 90 // Base chance if in Defensive posture
resCostPerDay = 10 // -10% for each day of marching
resCohCostPerDay = -1 // -1 cohesion for each day of marching
resModAdjGHQ = 10 // +10% if adjacent to army HQ
resModIsGHQ = 25 // +25% if the army HQ itself
resModLeaderStrat = 5 // +5% for each pt of strat factor of the leader
resControlChunkMod = 5 // Every 5% of MC lacking gives -1% chance (both for start and end region)

in this case the basic reason is the movement cost for the major river. Depending on offsetting factors, especially strategic skill of the commander, it can still happen but its very unlikely.

info is in 'gamelogic' in \settings

Thanks for the responses.

I've read that link before and I reread it just now. Twice before I had clear weather, good terrain, 4 or 5 rating in strategy, high MC, and an army stack involved. So lots of things to increase my odds of MTSGing, but didn't happen in those ones. A 3rd time was probably a marginal chance. I guess it was just a combination of bad rolls and a small sample size that lead me to the wrong conclusion. Now I know!

When I first bought the game, I started with the patch at that time and MTSG seemed to be less likely to me at least. I could be wrong...

Although since I have used the April '15 patch I have had consistent MTSG, which seemed to work every time. In fact I cannot recall too many instances of it failing. Although you never know...

Since the probability of a successful MTSG is influenced by movement cost, would the Traffic Penalty be a factor in the outcome?

I asked that in this thread and Pocus said "Yes".

http://www.ageod-forum.com/showthread.php?39716-Traffic-Rule-Explained

BattleVonWar wrote:I have had consistent MTSG, which seemed to work every time. In fact I cannot recall too many instances of it failing.

I get the same feeling about MTSG : always succesful. I can only remember of one (or 2) occasion where it did not happen. In AACW is was more common to fail the MTSG roll.

This is pure speculation but I wonder if in AACW the roll was made once per battle when it is done each round in CW2 ?

This statement may offer some additional insight:

"Stack in retreat or doing MTSG can't cross blockaded river or pass through 'front' because of ZOC."

http://www.ageod-forum.com/showthread.php?39344-gt-CW2-patch-1-05-available-NOW!-lt

So, does a fort or enemy stack blockade a river with its ZOC, preventing MTSG?