‘Hexing’ Horse and Musket One Hour Wargames

As many fine gentlemen before me, I felt the urge to convert OHW’s rules to play them on a gridded map. My main goal was to be able to play on a much smaller area than my sausage fingers allow when using free movement, with additional side benefits including being able to play online/by mail or similar method. Ideally, I wanted to stay as close as possible to the free movement rules described in the book – including subtle emergent effects and interactions between troop types, unit frontage/density, board to movement ratios, ‘road block’ effects etc. I’ve realized that most OHW scenarios are very carefully balanced, and messing with any of the above parameters would unavoidably bias it toward one of the sides… making them much less interesting. As the title suggests, I’ve only tackled the horse and musket period so far – I think this is the era in which OHW rules most shine (this will be the subject of a future post, I think). Without further ado, this is what I’ve come up so far.

The Board

This was easy. All OHW scenario maps are 36”x36” squares, divided in nine 12”x12” sections. Most terrain features are neatly aligned with this grid and span some multiple of 6” in both directions. In theory, either hexes or squares would work, but I prefer hexes for everything except ancient pitched battles. I chose hexes to represent 3” on the map, resulting in a 12x12 square arrangement of hexes.

[Side note: double-sizing them to 6” would still adequately represent OHW maps, but would be too coarse to represent some of the finer implications of the movement rules].

Unit representation

Here, the obvious choice would be to have each unit occupy one hex, but this would largely underplay the actual size of the units with respect to board size. In the rules-as-written, artillery must occupy a 2”-4” frontage, while all other units’ width is specified to be 4”-6”. This is actually important because the larger the units, the harder it is to concentrate firepower, coordinate attacks and form an ordered battle line. Since I always like a tactical challenge, I’ve opted to have all units at maximum size (4” for artillery and 6” for infantry, skirmishers and cavalry). Due to this, I play with all units occupying two adjacent hexes. Artillery is admittedly a borderline case, but I’ve found that having two different unit sizes needed a lot of extra rules overhead for little benefit – so I’ve accepted a (slight) overestimation of its frontage instead. Having units span two adjacent hexes also mean that their ‘centre point’ (as often invoked by the rules) can be univocally defined as the node connecting their two hexes on the front side.

[Side note: in the following discussion, when I refer to “part” of a unit I mean “at least one hex containing the unit”].

Ranges and front arc

Figure 1 shows how to calculate ranges to and from a unit. OHW requires most measurements to be performed from centre points (even though it’s often vague about where exactly the target point is, but I’ll discuss this later). Due to this, a somewhat counterintuitive result is that the only hexes at a 3” range are those adjacent to both the unit’s hexes. All other adjacent hexes are considered to be 6” away, then 9”, and so on. No further surprises here! Front arc can be easily defined as in figure; it’s the closest you can get to 45° with hexes and I don’t see any better options.

[Side note: when a scenario specifies that a unit must enter ‘from’ a given point, I play that the specified point is the front hex at 3” distance and measure movement consequently].

Figure 1: centre point (red dot), front arc (shaded area) and distance of hexes relative to a unit. Ranges beyond 12” are only needed for artillery shooting. OTOH, artillery range is so huge (150% of a board edge!) that it’s hardly necessary to actually measure it…

Movement

OK, this was a bit tricky to nail down. In OHW rules-as-written, moving a unit entails shifting its centre point along a straight line up to their movement allowance; unrestricted pivoting on the centre point is allowed at the start AND the end of the move. This creates a series of implications which one may or may not like (I think they’re kind of OK for horse and musket games); for example, you cannot go ‘around’ impassable terrain or units in one move; and pivoting at the end of the move effectively gives you a slight boost in terms of how far some part of the unit can travel in a move.

Another aspect to consider is that if you only allow one unit to occupy each hex, you artificially reducing the maximum density of troops achievable under standard rules. This is often relevant as several scenarios have units enter from a specified point such as a road; and maneuvering slow units out of tight spots can be extremely difficult if stacking is disallowed, resulting in ‘traffic congestions’ that simply wouldn’t happen with free movement.

To reflect all this, I define a normal (i.e. non-charge) legal move as a move in which:

1) At least part of the unit (see above) ends within its maximum movement allowance.

2) An unblocked straight path exists between the starting centre point and the final centre point. A movement straight path is blocked by any part of a hex (EXCLUDING hexsides and corners) containing terrain the mover cannot enter, and/or units the mover cannot pass through. In the horse and musket era, this mainly means that skirmishers ignore other units and woods when moving; and that all units ignore skirmishers. Only infantry and skirmishers can end their move being partly in a town; other terrain types work as described in the book, without hex conversion problems.

3) Exactly two friendly units can stack in the same hex (or hexes), but only if both have the same facing. Enemy units can never stack. The relative position of stacking units counts (i.e. one will be in front of the other; I can’t find the energy to actually write down rules for this, but it’s quite obvious that one of the two stacked units will be the only possible target of shooting/charges depending on the angle of attack).

Figure 2: examples of movement. Shaded hexes are those within infantry Unit #1’s 6” movement allowance. Unit #1 (move = 6”) can move to positions A and B, since they both result in part of the unit still being within movement range. The moving unit cannot pass through Unit #2 (so it cannot move to D), but it can still move to B because the movement straight path only touches the edges of a blocked hex rather than its interior. Unit #1 can move to C because it ends aligned (i.e. having the same facing) with Unit #2. It cannot move to E since the movement straight path touches the interior of an hex containing terrain it cannot pass.

Charges

In OHW, charges only differ from normal moves in just two respects: (1) pivoting is only allowed before moving, and (2) initial pivoting cannot exceed 45°. Point (1) means that you cannot use that ‘extra pivoting reach’ you usually get as a side effect of normal moves to contact enemies (that would definitely look silly). Point (2) can be also rephrased to “you can only charge targets in your frontal arc”.

A crucial point is that you actually have to reach your target with a charge! I know it seems trivial, but most grid adaptations I’ve seen allow melee attacks to be performed from adjacent hexes, while still requiring units to fire into target hexes. However, this messes up OHW unit balance completely: for example, it would allow horse and musket cavalry to frontally charge infantry and skirmishers without ever coming under fire, which is impossible in the rules as written.

Translating all this to hexes, a legal charge move must comply with these additional requirements with respect to a normal move:

1) A charge move must end with the whole unit within movement range (no extra 'pivoting' range for part of the unit at the end of the move)!

2) It must end with at least part of the charging unit in the SAME HEX as part of the target unit; facing is irrelevant since this does not count as stacking. [Side note: in the horse and musket rules, this brief occupation of the same hex by chargers and their targets is immediately resolved after rolling for casualties, since cavalry will either shatter their target or be repulsed].

3) At least part of the target unit must be within the charger's front arc at the start of the charge.

Charges to the flank and rear are adjudicated based on the target’s front arc: if at least part of the charging unit lies within the target unit's front arc at the start of its move, it's a frontal charge. If not, it is a flank/rear charge. Easy-peasey!

Repulsed cavalry charges

The book is quite vague about how exactly moving falling back units. I play that a repulsed cavalry unit must move ‘back’ to a position (1) fully within its original front arc, and (2) within 6” of the target hex.

[Side note: due to how charging and falling back work, I’ve found it’s much easier to just declare a charge without actually moving the cavalry unit, adjudicating its final position only after the charge’s outcome is known].

Figure 3: examples of charging. Cavalry Unit #5 can charge enemy infantry unit #1 since it can reach a hex containing part of it with a legal move fully ending within its 12” movement allowance (shaded area). It cannot charge Units #2 and #3 because the straight movement paths are obstructed by terrain (#2) or units (#3) it cannot pass through. An unobstructed straight movement path exists to Unit #4 (it only touches the corner of one hex occupied by cavalry Unit #6); however, the target unit cannot be reached with a legal charge move since it fully lies outside the cavalry’s 12” charge range. Unit #1 will count as attacked in the flank/rear; charges towards all other units would have counted as frontal (if they could be reached, that is).

Shooting

In addition to being stationary as per standard OHW rules, a shooter can inflict losses on a target unit if all of the following is true:

1) At least part of the target unit must lie within the shooter’s frontal arc AND shooting range.

2) An unblocked shooting straight path (aka LOS) must exist between the shooter's centre point and the target's centre point. LOS is blocked by any part of a hex (EXCLUDING hexsides and corners) containing enemy units other than the target, friendly units, and 'area' LOS-blocking terrain (woods, towns etc). LOS extends into (or out of) one such hex, but no further. Hills have a central crest which runs along hex sides; LOS is only blocked if it crosses the crest.

Figure 4: shooting examples. Infantry unit Blue#1 has not moved, and has as many as four enemy units at least partly within its front arc! However, it quickly realizes it cannot shoot Red#1, since it’s fully outside musket (12”) range. Red#2 and Red #4 are within shooting range, but neither can be shot since LOS is obstructed by a hex containing an enemy (#2) or friendly (#4) unit. A somewhat irritated musket staccato can be heard as Blue#1 begins shooting its only available target, Red#3.

Figure 5: more shooting examples (terrain and LOS). Again, Blue#1 is apparently spoilt for choice with regard to possible targets. Skirmisher unit Red#9 can be targeted (at half effect) since part of it is within front arc and range; LOS extends into the first met obstructing terrain hex. However, it cannot extend out of such a hex; due to this, LOS to Red#2 is obstructed. View of Red#3 is completely obstructed by the hill (LOS is blocked by the highlighted hill crest hexsides).

I’ve used these rules for several OHW horse and musket games without any particular problem – I think they work just fine. The first scenario I’ve tried with hexes was the excellent No.8 “Mêlée”, and it resulted to be extremely balanced through multiple replays – a good indication that no bias was introduced by ‘hexing’. Encouraged, I continued with other scenarios. I’ll post about this soon.

Figure 6 - OHW scenario #8 converted to hexes with terrain annotations - useful to get players on the same page prior to battle!