[Mass Combat] Cutting supply lines

[Michael Thayne]

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?

[Say, it isn't that bad!]

Originally Posted by Michael Thayne

Thoughts?

Maybe we need a GURPS: Mass Combat - Logistics?

[Polydamas]

Originally Posted by Michael Thayne

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.

[Polydamas]

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.

[Rupert]

Originally Posted by Polydamas

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.

[Polydamas]

Originally Posted by Rupert

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.

I think that would be reasonable.

Bowmen have Maintain 8k
Musketeers have Maintain 6k
Riflemen have Maintain 12k

Horse Archers have Maintain 30k
Cavalry Pistols have Maintain 20k
Mounted Rifles have Maintain 20k

So the higher-TL the troops, the more of their Maintain is fuel / ammunition / durable goods, and the less food and fodder and clothing. But this is really technical, the details are hard to research (especially for adventure-friendly situations like technicals and men with rifles, mortars, and HMGs moving across a failed state) and its likely to turn into the situation where 1 or 2 people in the group are really excited and everyone else is bored stiff. If you know enough to want to use detailed rules, you know enough to handle them narratively.

I would suggest that anyone interested gamify the scholarly books on the subject like:

Donald W. Engels, Alexander the Great and the Logistics of the Macedonian Army
Jonathan P Roth, The Logistics of the Roman Army at War
Martin van Creveld, Supplying Mars: Logistics from Wallerstein to Patton

There must be something on the logistics of indigenous forces in Afghanistan or the Libyan Civil War but I don't know what. If you understand logistics and GURPS, you can make something which models the specific situation your players got themselves in to, whereas building a general model which is simple enough for a game with fantastic elements and imaginary worlds is hard.

[Polydamas]

Originally Posted by Rupert

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.

Naval Logistics can support naval elements as well as land elements based in a port, and historically navies were a problem because they cost cash and there was no way around that. Agrarian societies are good at collecting and redistributing crops and cattle and fodder, not always as good at turning that into cash and hiring skilled workers and buying rare materials and finished goods with it. maybe they were thinking of something like that? Or data from 20th century militaries on tooth-to-tail ratios in armies, navies, and air forces?

[Polydamas]

A pretty typical means of cutting supply lines is having some fast-moving or concealable troops near the route and attacking things passing along it.

Another is the enemy having a superiority in light troops, so your men can't go out and collect fodder and grain without little groups being bushwacked.

Another is breaking key transport infrastructure (burning pontoon bridges, smashing bridges, digging up railroads, bombing airstrips). This is often harder in practice than in theory, but it makes for good adventure scenarios. Yuval Harari has a book with a chapter on a raid to destroy the mills that an army needed to grind its flour.

Its not necessarily about occupying a hex.

[Rupert]

Originally Posted by Polydamas

Naval Logistics can support naval elements as well as land elements based in a port, and historically navies were a problem because they cost cash and there was no way around that. Agrarian societies are good at collecting and redistributing crops and cattle and fodder, not always as good at turning that into cash and hiring skilled workers and buying rare materials and finished goods with it. maybe they were thinking of something like that? Or data from 20th century militaries on tooth-to-tail ratios in armies, navies, and air forces?

I'm just thinking that you can move a lot more stuff a lot cheaper by sea than land.

In WWII a liberty ship cost about $2,000,000 and had a nominal load of 10,000 tons (and often carried more). Roughly speaking, a Liberty ship could move that load about a 1,000 miles and then return in 10 days. So it could move 1,000 tons/day 1,000 miles.

To do the same on land via trucks you'd need about 800 trucks, which happen to cost about the same as the ship (They move faster, but are much, much smaller) (at about $2500 each at the time). Capital outlay for the hardware is much the same. However, the ship requires about 40 people, the trucks 1600, just for the drivers, so initial recruitment costs for the trucks is a lot higher.

Then there's maintenance costs - the trucks need 40 times as much food and pay for their crews. They manage to move their 5t load about 7.5 miles per gallon of fuel (on a road) if things go well (37.5 ton-miles per gallon). The ship manages only 0.04 miles to the gallon, but carrying 10,000 tons for over 400 ton-miles per gallon (over ten times the efficiency).

The same sort of effect occurs at lower TLs, with the added benefit for sea travel that's it's faster than moving things by cart or wagon.

At TL5+ railways help with land transport to an extent, but shipping still has it beat.

[Michael Thayne]

Originally Posted by Polydamas

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?