Siege Notes: (3a) Time Out for Some Arithmetic and Head Scratching...

 I mentioned previously that there were a couple of areas in my siege rules where I was going to have to make some estimates - sometimes the generally accepted numbers seem unlikely, and sometimes supposed experts quote each other, backwards and forwards, and legends are established. There are two priority topics requiring a bit of work at the outset - consumption (and therefore supply) of gunpowder and the digging of trenches; I felt it might be a bit much to just go off on one while walking through the rules, so I shall attempt to cover these in a little time-out session, and then with luck I can use the results to progress the rules discussion more gracefully.

How Much Gunpowder?

The immediate problem is to work out how much powder the two armies in a siege will need. OK - so how much do they use?

Here are some preliminary facts: Vauban says that a weapon firing roundshot requires a propellant charge of one-third of the weight of the shot; a barrel of powder weighs 100lbs; 22 barrels to the ton.

A couple of other givens: I shall ignore the powder used by musketry, but will attempt to allow for the powder inside shells; I will also have to get around to allowing for powder used in mines and (maybe) petards; my starting intention is that the garrison has a known powder store at the start, and has to husband that during the siege, while the battering train normally carries 2 weeks' supply with them (that's 4 turns) and the visiting Commander will have to arrange for regular deliveries as the siege proceeds - this last bit will require some careful thought...

What do we know? Well, I've done a lot of reading (John Jones, John May, Alexander Dickson, B P Hughes, J V Belmas, David Chandler, Chris Duffy...) and I found a lot of numbers. 

For a start, it is widely quoted that experienced gunners could maintain a rate of between 20 and 30 shots an hour without problems. Oh really? For how long?

I'm going to look at the main siege weapons, 24pdrs. Let's assume they have shifts standing by to keep the rate of fire up. The guns require to be thoroughly sponged and cleaned out about every 30 shots, the shifts need a little time to change; the guns will not just be firing - they will occasionally be re-deployed, and the peak rate of fire will be when they are concentrating on creating a breach; at other times they may be used picking out tactical targets, to clear the area opposing an attack.

There is a very interesting account of some trials conducted at the Royal Arsenal (London) in 1813, in which guns were fired continuously - batches of 50 shot spaced at 3 minutes between shots. This experiment was to compare the difference in enlargement of various types of vent ("common" - cast iron? - wrought iron and copper). The guns involved in the tests would be standing calmly in the open, with master gunners, not under fire, and not constrained by firing through an embrasure. One thing that comes immediately from the tables is that the wear is significantly less when the shots are spaced at 4 minutes. These tests were with iron guns, which were regarded as more hard-wearing than brass and less likely to droop if they overheated, though they had a greater tendency to burst...

4 minute spacing gets us down to 15 shots a minute, and regular cleaning and other overheads might get us down to 10 - maybe that's a decent starting figure as an average. OK - so how long would they be firing each day? No doubt it varied, depending on the task of the day.

I found some interesting returns from the Peninsular War - artillery officers were obviously devoted to counting things. I spent some time looking at Wellington's "Second Attack" on San Sebastian. There are no analyses of shots fired each day, but Dickson dutifully records that the 24pdrs, of which there were 28, fired almost exactly 28000 shot during the 5 days of the main attack - they started battering the fort on 26th August 1813 and they stopped on 30th, in time for the infantry assault on the 31st. This average of 1000 shots/gun for the 5 days is so devastatingly convenient (!) that it did rather dominate my calculations thereafter! We know that 7 of the guns were in a separate battery, which was found to be ineffective, and were shifted to join the main effort against the breach, so some moving about was included in the 5 days.

Righto - let's take the overall numbers. 1000 roundshot per gun over 5 days gives 200 a day. My guessed average rate of 10 shots an hour (which already includes some maintenance and changes of shift) would require 20 hours for 200 shots. It's a long day, but maybe we are heading in the right direction.

A quick check with the rules: guns firing roundshot may opt to use what I have called "continuous" fire (better terminology probably exists) when they are really trying very hard (completing a breach would be such a time). Continuous fire gets you extra dice to fire with, but uses powder at a scary rate and also introduces the possibility of damage to the guns as they overheat, so the idea is that it is something you don't do if you don't need to. 

In my rules, a gun model represents a half-battery of 3 pieces, and a turn is a half a week (so 3.5 days). 

Let's see how our 200 shots a day figure average works out. Vauban's estimate of one-third of the shot poundage works very nicely with a 3-gun half-battery - a model 24pdr on the table will require 24lbs per single volley, which is very close to a quarter of a barrel, and therefore a full barrel every 4 volleys. A turn is 3.5 days at 200 volleys, which is 700 volleys, which works out at 175 barrels. Interestingly (convenience strikes again), at 22 barrels per ton, 176 barrels would be exactly 8 tons. 

Now I've been working with this system for a while, and, in the absence of better terminology, I've informally defined a "Load" of powder as "the amount of powder consumed by a model 24pdr firing for 1 Siege Turn", and I know that a model gun is really a half-battery of 3. "Load" is not a good word - perhaps it is short for a "Wagon Load" or something, but I know what I mean, and it's simple to work with. If (say) the Garrison is expected to hold out for 8 weeks (16 turns), then each model 24pdr will need 16 Loads in the magazines to last the duration.

My rules stipulate that a 24pdr (model) firing during a Siege Turn will  be marked with a "Puff" of cotton-wool. This indicates that it has fired, and at the end of the Firing phase the "Puffs" will be collected in, added up and converted into a deduction from the powder store; 1 Puff indicates consumption which requires to be replenished by the delivery of 1 Load of new powder to the 24pdr gun. My housekeeping calculations have been in Puffs/Loads, which are (interchangeably) the same amount. There is also a smaller size - a half-puff - which represents the consumption of half a Load [4 tons] of powder. 

[It is possible that, in the interests of simplicity, I will continue to use the Puff/Load measurement system; the only new information coming from the calculations above is that I now know that a Load actually weighs 8 tons. There would be a touch of elegance in multiplying all the numbers by 8, and dealing in tons, which is a real weight which anyone would understand. I offer this simply as a matter of personal preference; you might even consider multiplying by 176 instead of 8, which gives the amounts in barrels, which feels even more authentic. The downside is that the arithmetic becomes more of a chore, the numbers less memorable - maybe the whole thing moves another step nearer to a clerical job rather than a pastime? With a little extra work, you could convert the amounts into buckets, or teaspoons, which would guarantee you a lifetime award of the Bruce Quarrie Medal for Spurious Accuracy (BQMSA). Sorry - I digressed a little there - this is entirely a question of what you like; personally, I consider that pocket calculators, like tape measures, are things I don't really wish to see on my tabletop.]

A 12pdr field gun will use half as much powder as a 24pdr, so that's a half-puff each turn; let's assume that a standard mortar uses the same powder as a 24pdr, if we include the powder in the shells, but only half that amount if it is firing stones; a heavy mortar will use 1-and-a-half puffs firing shell, but only 1 puff if firing stones; a little Coehoorn mortar, which fires short-range fragmentation grenades, is probably most likely to be used during a Tactical Turn, but in a Siege Turn would consume half a Puff. 

Let's add up the requirements, then, for a complete Garrison. We'll now talk in terms of models, not half-batteries, for simplicity. Say they have three 24pdrs, two 12pdr field guns and two standard mortars - the requirement for a turn, if everyone is firing, would be:

3 @ 24pdr                      3 Puffs
2 @ 12pdr                      1 Puff
2 @ Mortar                    2 Puffs
                                     -----------         
Total                              6 Puffs [48 tons] per Turn; 96 Loads for a 16-turn siege 
                                      [768 tons] 

Thus the Governor needs 96 Loads in his magazines; the preliminary audit should be adjusted by rolling 2D6 and applying the Randomizer table [mentioned in Section 3 of Siege Note (3)]; if the Governor is not happy with the result, he may choose to re-roll the Randomizer, but he must accept the re-roll.

That is quite straightforward, and is all settled (secretly, if necessary) before the siege commences. The powder store in the fortress will be depleted by each turn's powder usage (count the Puffs), and possibly by Event Cards and Espionage activity. Remember that artillery firing roundshot may opt for Continuous Fire in a Turn, which doubles powder consumption and also effect, but also risks overheating the guns.

Misfires, which don't hit anything, still consume powder as usual.

What about the Besiegers? For this same 16-turn siege, we assume that the train will carry 2 weeks' (4 turns') powder with them, and then a regular supply starts from Turn 5. At the start they arrive with

6 @ 24pdr                      6 Puffs
3 @ 12pdr                      1.5 Puffs
1 @ Heavy mortar         1.5 Puffs
4 @ Mortar                    4 Puffs
                                     -----------         
Total                              13 Puffs [104 tons] per Turn; 52 Loads for the 
                                      first 4 turns [416 tons], which has to be Randomized
                                      in the normal manner 

Subsequent deliveries:  The scenario may set conditions here, depending
                                      upon how hostile the surrounding countryside is, 
                                      how difficult the supply route. In this case, the 
                                     Besiegers should arrange a regular delivery of 13
                                     Loads each turn (Randomized on arrival); the scenario
                                    may also stipulate that a Randomizer roll of any double
                                    (or selected doubles) means that the delivery fails to 
                                    arrive. If the Digging Standard is currently 6 (or higher), 
                                    the shipment will not normally arrive. No-one said this 
                                    was easy.  

In all of this, the results should be secret for a competitive game, and the Commanders have the usual entitlement to a single re-roll (which is binding) for any Randomizer use.

That's certainly quite enough about gunpowder, but it will reappear when we get to the Firing rules.

 

Trenches - How Fast, and Who Digs Them?

 

Sapping - specialist work

 

The Vauban's Wars rules have all digging being done by Sappers, which doesn't seem right to me. What I have read suggests that the Sappers did the specialised digging of forward saps, but the main body of the labour of making trenches and redoubts was provided by the Poor Bloody Infantry (who else?), or else by gangs of civilian contractors (slaves?) - an alternative which I haven't managed to work into the game as yet.

 

According to Chris Duffy, work parties of infantrymen would advance after dark to the site where the digging was to be done (eye witnesses say that these gangs might be up to 3000 men, but 1200 is mentioned as a sort of average - handily, this is about 2 battalions in my game...). The location would be at the current heads of sap, and the men would carry fascines (to mark out the line of the new trench) and digging tools. They would place their fascines as instructed by the engineers, would form a line about 2 paces behind the fascines, with 2 paces between each man, and would start digging, excavating a trench about 1 metre deep, and piling the spoil up between the forward edge of the trench and the fascines. There was an obvious motivation to get this work to a stage where the diggers were in cover before the sun came up!

This is all fine, but I need a few numbers to see how it works. The hexes on my battlefield are 200 paces across, which implies a line of 100 men stretched across, digging furiously. In such a line, a battalion could theoretically attempt a trench on a ridiculous front - 6 hexes - 1200 paces. No - such a sparse line would be very vulnerable to a night-time raid, the men could not dig for much more than a couple of hours at a time - maybe less than that. I've adopted a system where a battalion (600 men) placed in a hex would at any moment have 100 men digging, and 500 waiting to relieve them, carrying stuff about and (importantly) standing guard. In fact, half a battalion could probably handle a hex-width of trench like this.

One of my Siege Turns represents half a week, so the working crew have the dark portions of 3.5 days to complete the digging, tamping down, widening and reinforcement of a section of the parallel. Normal practice was to replace them with another regiment at the end of each shift. Is it simply a foregone conclusion that they will finish the work? Well, very bad weather might stop them, as might some initiative on the part of the Garrison. The fortress gunners could put up a star-shell, and then fire on the working party - if they can afford the powder, and for as long as the star-shell burns. After the embryonic trench reached about 2 feet deep, the diggers could lie down and be in cover - it would be an interruption though. If the diggers had lots of armed friends, they could probably see off any kind of sortie or trench raid.

A number of rule sets make completion of a trench section automatic if you get the diggers into the right place. I've thought my way back and forwards on this. One argument against guaranteed success for me is that my Vauban forts all look pretty similar, and the standard approach to conducting the siege might often look similar too. Suppose all my Louis XIV period sieges consist of

* Dig 1st Parallel 1200 paces from the Covered Way
* Send forward 3 zig-zag saps
* Dig 2nd Parallel 800 paces from the Covered Way 
* Add emplacements for heavy guns to eliminate the Garrison's guns
* Add emplacements out to one or more flanks, to provide ricochet fire to enfilade the faces of the bastions adjacent to the intended breach site
* Etc

At this stage, the only differences between this siege and the last one I played out might be the chance variations in fire effect, and maybe the odd Event Card. The idea of always getting to the same situation horrifies me, first because it isn't necessarily authentic, and second because it makes the game rather pointless. Having thought about it (again) I am currently back in favour of having a chance element in the completion of the siegeworks - that produces some extra variety. The soldiers succeed by beating the current Digging Standard (DS) with die rolls (and they get extra dice if they have an Engineer handy); they'll probably manage it - especially if the DS is low, but if they don't they are left with a section of the trench which is incomplete - it may be a botch-up of gabions and whatever they have to hand, but if the end of the Siege Turn shows that some of the trench sections are in this state, then the soldiers in them will be only in soft cover, and potentially in trouble. They will attract a lot of attention when the Garrison gunners have their turn.

 

Digging Standard die clearly on view in an ECW siege

 I'll talk about this again when I walk through the Digging rule. 

To finish off this time-out note, I'll mention Duffy's Sandhurst Kriegspiel Society game, as described in his Fire & Stone book. Under those rules, forward saps were advanced at a prodigious speed, and a party of infantry, with an officer present, would be crammed into the sap, where they would be fired upon by the garrison artillery. Provided the officer and at least 50% of the infantry figures survived, they could then be placed in position to dig a section of parallel, and the new trench would be placed along their length. The detail of what was going on is maybe not how you or I might have played it, but it attaches a chance element to progressing the siegeworks; as I sit here today, I am in favour of this chance element. Anyone who has had the experience of seeing landscape gardeners arrive in the morning, and then coming home after work assuming that everything will have gone well, may appreciate my preference.