A discursive look at Napoleonic & ECW wargaming, plus a load of old Hooptedoodle on this & that

Thursday, 17 November 2011

Sieges in my Solo Campaign Rules

This is getting into serious Nerd Territory, so be warned. I’d been thinking about the subject anyway, and was prompted further by Clive’s posting of Paddy Griffith’s algorithmic system for simulating sieges.

The background to this is hinted at in my previous post on my developing solo Campaign Rules for the Peninsular War. Well – not The Actual Peninsular War, of course, but a similar sort of war in the same area, using similar troops, around the same time.

They had a lot of sieges - it was a feature of the warfare. It would be lovely to be able to trundle out my model fort and fight siege games as part of a campaign, but sadly it is not practicable. The campaign has a weekly turn, and an ongoing siege would almost certainly last a number of turns. For a while I considered the possibility of maintaining a table-top siege game while the map moves went on in another room (or something), but that stopped abruptly when I realised that two or more sieges might be running simultaneously – and what then, eh?

So - like it or not - sieges are going to have to be settled by mathematical means, off the table. I have a copy of the NapNuts campaign rules, which handle sieges by means of A Duckenfield’s rules which were first published in Practical Wargaming – in fact his rules are lifted straight in, which is probably a vote in their favour. Being an awkward sod, I decided to set up my own system, though it is on not dissimilar lines.

I need the off-table siege “game” to give realistic durations and casualty levels for the siege operations, and I need it to produce reasonable results, but to operate crudely enough to work without destroying what is left of my poor brain (or enthusiasm). My earliest drafts were far too complex – this is about the fourth redrafting, and I am sure it has some distance to go. The trend has been toward progressive simplification throughout. I have glossed over many things – some because it was convenient to do so, and – doubtless – some because I just hadn’t thought of them.

This is where I have got to. It’s not finished by a long chalk, but it’s coming along. If this is the sort of thing you like, you may well like this.

Sieges in the Campaign Rules

The turns are 1 week long.


Certain of the Areas on the map contain towns which are fortified and have a Fortress Value (FV). This reflects the size, strength and position of the installation, plus (amongst other things) an allowance for some resident artillery. The initial FV may subsequently be reduced by a combination of factors – damage to the walls, loss of guns, being compromised by siege works and siting of batteries – anything which renders the place less formidable.

The fortresses on the map, with their FVs, are:

Abrantes (P)           4
Alicante                  8
Almeida (P)            5
Badajoz                  8
Barcelona               8
Bayonne (F)           6
Bilbao                    6                              Towns marked (P) are in Portugal, (F) are in France
Burgos                   7
Cadiz                     12                           This is not intended to be a complete historical list -
Cartagena              10                              it is drawn up simply for the game!
Ciudad Rodrigo      6
Elvas (P)                5
Figueras                 8
Gibraltar                15          
Granada                 7
Jaca                       4
La Coruna              8
Lerida                    6
Lisboa (P)              7
Pamplona               6
Perpignan (F)         6
Sagunto                 10
San Sebastian         7
Santander               6
Tarragona               8
Tortosa                  6
Valencia                 7
Vic                         7
Zaragoza                7

Fighting troops in the fortress contribute a Garrison Value (GV). The number of units stationed in a fortress may not exceed its basic FV. For this purpose, a unit is a battalion of infantry (strength usually 4 CCN “blocks”) an artillery unit (3 blocks) or cavalry regiment (3 or 4 blocks). Initial GV is equal to the number of units (though cavalry and militia count 1/2 each), and its reduction during a siege will represent both casualties and diminution in “resolve” of the garrison. GV may be increased by a further 1 if the garrison commander is an identified Leader rated as Good or Outstanding (2 or 3).


The besieging troops are not limited in number, though supply may be an issue. The initial Assault Value (AV) is equal to 1/4 of the number of fighting units present (rounded to the nearer, half up), and may be increased by 1 if the overall commander of the besieging force is Good or Outstanding. The Battering Value (BV) is simply the number of specialist siege batteries present – these may be battering guns, mortars or rockets.

Thus, at the start of a siege, the defenders will have a FV and a GV, and the attackers will have an AV and a BV. These factors may all be impacted subsequently by enemy action.

If FV becomes zero, the fortress can be entered at will and the garrison will surrender.
If GV becomes zero, the garrison is no longer able to resist, and any survivors will surrender.
If AV becomes zero, the besieging force is no longer able to continue.
If BV becomes zero, the attackers have no bombarding artillery available, and will normally call off the siege (unless they expect some to arrive!).

If AV + BV is less than FV + GV then the attackers will normally call off the siege.

Each turn (commencing at the end of the first week of siege), the procedure is

Bombardment phase (all bombardment is simultaneous, so don’t make any deductions for hits until both sides have fired - the dice throws include the effect of accidents and bad breaks as well as direct hits).
* Defender throws [GV]D6 (i.e. a handful of 6-sided dice, GV in number) – any 6s will put a siege battery out of action (reduce BV by 1 for each), any 5s cause loss and demoralisation to the attackers’ forces and engineering (reduce AV by 1 for each).
* Attacker throws [BV]D6 – any 6s will damage or compromise the strength of the fortress (reduce FV by 1), any 5s cause loss and damage to the garrison and their resolve (reduce GV by 1).
* Adjust FV, GV, AV and BV for bombardment.

Protocol phase
If besiegers have not abandoned the siege, and if the fortress has not automatically surrendered, the attackers may summon the fortress to surrender. If AV > FV + GV + 5, then the fortress should at least consider surrendering, since they could not withstand a storm. However, a storm would kill more of the besiegers, and, if the defenders are French, they will be aware that the Emperor has given strict orders that no fort may surrender until it has withstood at least one assault....

The besiegers may elect to storm the fortress.

Storming phase
Defenders’ Storm Strength, DSS = FV + GV + 1D6
Attackers’ Storm Strength , ASS = AV + 1D6

* If ASS >= DSS then the fortress falls and the garrison surrenders. Attackers lose a final, further ½ GV from AV.
* Otherwise, if DSS–ASS is positive, storm is repulsed; attackers lose (DSS-ASS) from AV; defenders lose ½ this amount from GV
[Remember that losses in GV and AV are not just casualties – they represent all manner of loss of ability to continue].

Whenever it is necessary, at any moment during the siege (or when the siege is broken off or completed), actual casualties may be computed as one tenth of  the %age loss of AV or GV since the start of the siege.

Example – if successful besieging force started out with AV = 8, and end with AV of 6, then they have lost one tenth of 25% = 2.5% of the total force present.

Relieving forces will cause the besiegers to break off the siege, or at least divide their forces.

Sorties are abstracted as part of the unpleasantness which the defenders can inflict during the Bombardment.

Thus far, I have not explicitly addressed the question of the defenders’ supplies....


  1. Apologies to anyone who has had a look at this already and is now bewildered. It was very late when I posted this, and I should have waited until this morning. I got into some editing confusion with my cutting and pasting, and screwed up - I have now fixed it, so the bit about Garrison Value now reads correctly.

    The initial GV for the occupants of the fort is simply the number of combat units present, with some fudging for cavalry and militia and leadership. The Assault Value for the besiegers is ONE QUARTER of the units present - I got these two muddled up.

    I need to do some more worked examples to see if the numbers work out OK. More later. I'll need quite a lot of dice - well, it is a siege.


  2. Looks good to me. I kept thinking "what about..." and then finding it dealt with. For myself I might stipulate that at least 1 pt of the BV must come from battering guns rather than rockets and mortars.

    If I ever get organized enough to run a proper campaign may well steal it in part ot whole.


  3. Ross - agreed - absolutely. If there isn't a sensible proportion of proper, heavy battering guns in there then they don't get to damage the walls - so 5 hits the garrison, but 6 gets you nothing! How's that? No-one gets to flatten the walls of some biblical place like Cartagena with boy scout kit like rockets!


    Tony the Fort Buster