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Old 08-28-2020, 10:24 PM   #1
Michael Thayne
 
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Default [Mass Combat] Cutting supply lines

While Mass Combat mentions that land logistics troops require that "a clear supply line can be traced back to home base", it is a little unclear what this means. Movement speeds are mostly given in increments of 5 miles per day, so it's tempting to assume a map with 5 mile hexes and that a single element can render a hex unusable for purposes of tracing supply lines. It also seems like if supply lines can't be cut by enemy units, there's little point in using air logistics troops, unless you're supplying troops that have been paradropped into Mordor or something.

On the other hand, maybe cutting supply lines is meant to be outside the scope of Mass Combat, because it's unclear what the game effects would be. It's not actually true that all military forces everywhere suffer dramatic breakdowns in effectiveness after going a month without resupply—many would, but there are tons of historical exceptions from (the Mongols, ocean going ships in the age of sail, Sherman's march to the sea, etc.) So maybe this is just totally outside the scope of the system.

Thoughts?
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Old 08-29-2020, 01:07 PM   #2
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Default Re: [Mass Combat] Cutting supply lines

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Originally Posted by Michael Thayne View Post
Thoughts?
Maybe we need a GURPS: Mass Combat - Logistics?
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Old 08-29-2020, 02:17 PM   #3
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Default Re: [Mass Combat] Cutting supply lines

Quote:
Originally Posted by Michael Thayne View Post
While Mass Combat mentions that land logistics troops require that "a clear supply line can be traced back to home base", it is a little unclear what this means. Movement speeds are mostly given in increments of 5 miles per day, so it's tempting to assume a map with 5 mile hexes and that a single element can render a hex unusable for purposes of tracing supply lines. It also seems like if supply lines can't be cut by enemy units, there's little point in using air logistics troops, unless you're supplying troops that have been paradropped into Mordor or something.

On the other hand, maybe cutting supply lines is meant to be outside the scope of Mass Combat, because it's unclear what the game effects would be. It's not actually true that all military forces everywhere suffer dramatic breakdowns in effectiveness after going a month without resupply—many would, but there are tons of historical exceptions from (the Mongols, ocean going ships in the age of sail, Sherman's march to the sea, etc.) So maybe this is just totally outside the scope of the system.

Thoughts?
Modelling logistics requires detailed maps and lots of arithmetic, so for a little PDF GURPS Mass Combat's rule sounds OK. The details depend a lot on scale (supplying a few hundred troops is different than supplying tens of thousands) and TL (a TL 0 army can manufacture most of what it needs, a rich TL 8 army not).

I would not say that a single element can render a hex unusable, they need to be proportionate in strength to the size of the convoys they will be attacking or blocking. And the difference between rebels holing up in a key pass and building a wall, and mounted raiders rushing out of the tall grass to hit a hard of cattle being driven to your army, gives the players different stories to tell and decisions to make.

If the enemy's troops have Air Logistics, the players can't occupy that strategic pass and hold it until the enemy have to break the siege of the Last Free City (they might make a treaty with the wind wizards to summon terrible storms though ...). If the players' troops have Naval Logistics and they hear about something inland, they have to make hard choices. GURPS Mass Combat is about putting a skin of mechanics around a skeleton of story, given that in a typical group only 1 or 2 people are really interested in playing out technical military stuff for hours on end.
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Old 08-29-2020, 02:30 PM   #4
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Default Re: [Mass Combat] Cutting supply lines

Also, some of the Mongols' biggest defeats (Ain Jalut, the invasion of Japan) were due to logistics. Their strategy of bringing a herds of horses with them and living off their milk, blood, and meat only worked where there was lots of fodder to feed those horses. They needed fresh arrows, and if they wanted serious siege engines or bridges then they needed to bring up materials to build them.

GURPS Mass Combat pp. 13, 14 has a simple, clear, and reasonable set of logistics rules that a GM interested in the details can expand. If your army is transported to another world, its Land Logistics break with the penalties described on pp. 13-14. If it was supplied through a port and the fleet is sunk, its Land Logistics break. If after the battle for the Dwarf Kingdom it invades the Cloud Castles of the Giants, its Land Logistics break.
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Old 08-29-2020, 05:09 PM   #5
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Default Re: [Mass Combat] Cutting supply lines

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I would not say that a single element can render a hex unusable, they need to be proportionate in strength to the size of the convoys they will be attacking or blocking.
Hmmm. Maybe require TS equal to say 5% of the LS then? Possibly divided by length of the supply in hexes or something like that?
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Old 08-29-2020, 05:13 PM   #6
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Default Re: [Mass Combat] Cutting supply lines

Note that the question here is not just about how to handle PCs cutting supply lines—its also about how to handle PCs declaring they wanna pull a Sherman's March. If supply lines are not actually cuttable, and what matters is just having the money to pay for a logistic force, the maybe the difference between actual supply lines vs. extensive preparations to live off the land is just a matter of roleplaying with no game-mechanical effect. If supply lines are cuttable you have to come up with a better answer.
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Old 08-29-2020, 05:17 PM   #7
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Default Re: [Mass Combat] Cutting supply lines

Quote:
Originally Posted by Michael Thayne View Post
While Mass Combat mentions that land logistics troops require that "a clear supply line can be traced back to home base", it is a little unclear what this means.

Thoughts?
I think it is very hard to define precisely. Personally I read Logistic Force as the ability to get 'everything that is not war but it is important to war'. So anything that hinders it counts. Sometimes a force is 'cut' even if near home, like Gaius Flaminius' against Hannibal (Transimene). In other contexts, even if an army is deep into enemy territory, like Hannibal in Italy, or the Vikings in Northumbria, and there is not a 'line to their home base', they are not 'cut' if their logistic force can pillage, or make commerce.

And there are some events that could be modeled as an enemy 'cutting your supply lines' even if they did not cut them strictu sensu. For instance, let's say there is an army that has been pillaging his way up to a point. While the army is occupying a hill for a pitched battle, his enemy raids their camp and steals all the gold, running south. The army is still, able to get food from farms, or wood, but most likely, troops will feel as if they have 'been cut' and are likely to desert. That actually happened in the Battle of Tours(732), Charles Martel's forces managed to raid Abdul Rahman's camp. When the news that the gold they had pillaged before was being stolen, units started to flee during the battle.
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Last edited by condor; 08-29-2020 at 05:19 PM. Reason: comma, english
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Old 08-29-2020, 05:19 PM   #8
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Default Re: [Mass Combat] Cutting supply lines

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Originally Posted by condor View Post
I think it is very hard to define precisely. Personally I read Logistic Force as the ability to get 'everything that is not war but it is important to war'. So anything that hinders it counts. Sometimes a force is 'cut' even if near home, like Gaius Flaminius' against Hannibal (Transimene). In other contexts, even if an army is deep into enemy territory, like Hannibal in Italy, or the Vikings in Northumbria, and there is not a 'line to their home base', they are not 'cut' if their logistic force can pillage, or make commerce.

And there are some events that could be modeled as an enemy 'cutting your supply lines' even if they did not cut them strictu sensu. For instance, let's say there is an army that has been pillaging his way up to a point. While the army is occupying a hill for a pitched battle, his enemy raids their camp and steals all the gold, running south. The army is still, able to get food from farms, or wood, but most likely, troops will feel as if they have 'been cut' and are likely to desert. That actually happened in the Battle of Tours(732), Charles Martel's forces managed to raid Abdul Rahman's camp. When the news that the gold they had pillaged before was being stolen, units started to flee during the battle.
These are good points. I feel like some of these actions are meant to be handled by the "raid" strategy, except I'm not sure it actually captures them terribly well.
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Old 08-30-2020, 01:35 AM   #9
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Default Re: [Mass Combat] Cutting supply lines

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Originally Posted by Polydamas View Post
GURPS Mass Combat pp. 13, 14 has a simple, clear, and reasonable set of logistics rules that a GM interested in the details can expand. If your army is transported to another world, its Land Logistics break with the penalties described on pp. 13-14. If it was supplied through a port and the fleet is sunk, its Land Logistics break. If after the battle for the Dwarf Kingdom it invades the Cloud Castles of the Giants, its Land Logistics break.
Having a quick read through them, I'm not sure that Sea logistics forces should cost twice land logistics per unit of troops supported - sea transport is cheap compared to land, and always has been.
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Old 08-30-2020, 03:30 AM   #10
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Default Re: [Mass Combat] Cutting supply lines

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Originally Posted by Michael Thayne View Post
Hmmm. Maybe require TS equal to say 5% of the LS then? Possibly divided by length of the supply in hexes or something like that?
Michael, I would say it depends on the terrain and the infrastructure. Blocking a one-lane wagon road over high mountains is easier than blocking the open steppe. Blocking supplies to a big army is easier than blocking supplies to a small one (the big army may depend on a single railway).

In many cases there will be troops protecting supply lines which are beyond the scope of GURPS Mass Combat, which focuses on the forces commanded by PCs. Its only with the telegram and the trained general staff, and then really with the portable radio, that commanders can execute control over troops more than a few hours' ride or sail away. Usually, the PCs force will be part of a larger operation and transport network. And do you really want to worry about the location of storage depots, the timing of convoys and columns of replacements for casualties, and all that technical stuff which determines where these troops are at a given moment?

Quote:
Originally Posted by Michael Thayne View Post
Note that the question here is not just about how to handle PCs cutting supply lines—its also about how to handle PCs declaring they wanna pull a Sherman's March. If supply lines are not actually cuttable, and what matters is just having the money to pay for a logistic force, the maybe the difference between actual supply lines vs. extensive preparations to live off the land is just a matter of roleplaying with no game-mechanical effect. If supply lines are cuttable you have to come up with a better answer.
A pretty common premodern logistics strategy is telling a bunch of merchants what you will need and letting them sort out the details. That has two big limits: there still has to be enough food and fodder within transport distance of your army, and they can't handle reinforcements or specialized things like ammunition so well. In those cases, I would treat wherever those merchants are buying and stockpiling as "home base."

A pretty common premodern logistics strategy is getting supplies, animals, valuables, and personnel from locals (occasionally even paying them for them!) A big problem is that you can't get blood from a stone: there is only so much available, and only so much can be gathered over typical low-tech rural transport networks.

If I were writing foraging rules, I would probably let a reasonable roll support TL 0-4 forces up to one order of magnitude greater than the typical local settlement. In Iron Age Europe a few hundred men can roam freely between hamlets of a few dozen people, in a river valley with a tel every few miles or a coastline with a port on every bay you might support up to a few tens of thousands. There would be a steeply increasing penalty for each subsequent month within say a 20-mile radius. The numbers would start to look dicey at TL 5 and TL 6, and impossible at TL 7+, especially for troops more expensive than Riflemen.

You could get a substantial bonus if you are willing to pay cash money and its a society with commerce.

There would be a penalty if its the kind of place where everyone has a walled village, a hidey-hole in the jungle, or a place to bury their grain and the locals have warning and chose to resist.

I would look closely at Sherman's March to the Sea, how many casualties the Union took, what they had to leave behind, and how close they were to disaster when they finally took Savannah. Wikipedia gives the dates as 15 November to 21 December. Mass Combat p. 7 says "These values are measured in $, but in practice – especially at low TLs – many commanders “pay” part or all of these expenses by conscripting civilians, appropriating mounts and vehicles, and foraging, pillaging, and looting."

In a GURPS game, I would have scenes gathering up money, transport, ammunition, negotiating with major NPCs and the President, etc. Then the army leaves Atlanta and its Land Logistics no longer have contact with friendly territory. No later than 1 December, Maintain comes due, possibly adjusted for Maintaining a Force in Bad Terrain. I would roll for how much the army foraged up, but the army would probably drop to Low Readiness or No Maintenance. Fortunately, the Confederate forces have their own troubles, and with some good Strategy rolls, clever problem solving by the character with engineering skills, and interaction with major NPCs the players take the port and the supplies stored there. By January or February the Union has delivered enough Naval Logistics to support the force at Savannah. So the very simple two and a half pages of rules in GURPS Mass Combat can handle this.
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