Napoleon's Battles was designed to game war at the grand tactical level. In essence, the player is only impersonating a high-level commander and taking only the kind of decisions for which these ranks were responsible. That means that single battalions (and their handling and tactics) are not directly represented in the game, and that decisions that go beyond the game unit size are not his responsibility and out of his scope. The exact formation, placement and handling of lower-level formations (such as battalions, squadrons or artillery sections) are handled by lower echelon commanders, and its reflection in the battle is mainly handled by the random dice rolls.
In tactical-level rules, the usual method by which these lower level tactics are presented is in the exact placement of the manoeuvre unit components. As an example, the normal manoeuvre unit is a brigade, which is in turn formed by typically two to five battalions (depending on the year, nationality and campaign). This subdivision is not reproduced in Napoleon's Battles and, despite the brigade being represented by a block of figures, it does not represent a solid phalanx. The rules state that there are empty spaces between the battalions, skirmisher companies and even small cavalry or artillery elements attached in close support. The player does not have any control over the placement or the tactical use of these elements in his role of a high-echelon commander, and the area covered by the units’ bases is an influence zone that is firmly under control of the unit, rather than the physical space occupied by the soldiers in the unit.
However, because the rules indicate there is a lot of unoccupied space, it is tempting to assume that units can freely pass through other units because of the gaps between companies and between battalions.
We can make calculations, taking into account the prescribed space that soldiers occupied in formation and the size of their unit. As an example, we represent in the diagram a Napoleon's Battles unit with 4 bases using a scale of 1px per 1 yard. This roughly corresponds to three infantry battalions (at a 'half-distance' column, but other prescribed columns could be represented by this graphic) and half an artillery battery. It is true that the soldiers would not have been crammed solidly into the whole area, but we can see that there is not much empty space left (and this does not take into account other small features that may appear in the area, such as single houses, clumps of woods or other obstacles too small to influence the grand-tactical game, but still present anyway).
This example (and similar calculations) show that the space covered by the unit is not sufficiently empty as to allow units to pass freely through it. In previous editions, there was no restriction to this interpenetration and units could freely pass through each other. We judged, even before becoming involved in the 4th Edition project, that this was a rule that should be modified, and we discussed this issue with Bob Coggins for a considerable time. It is true that the units could open ranks, allow passage through the gaps and form again or break into narrow formations and reform again later, but this would essentially be a formation change, which would prevent most units from finishing the movement under the Napoleon's Battles rules (both in this edition and in the previous editions).
Average infantry units can move 1” after changing formation, and hence, for many infantry brigades, it would be impossible to make this movement; but these are the same infantry brigades that can only move 100 or 200 yards in 30 minutes while in line formation (it is generally accepted that this figure represents a good average for the Era). This game (as it was conceived by Bob Coggins & Craig Taylor) heavily punishes the movement of infantry units in formations other than column. Re-forming, dressing the lines, and changing formation, heavily reduce the movement of infantry units (ranging from 10% to 20% of the column movement factors), and a whole brigade passing through another brigade was similar to a formation change (not passage of lines at battalion level - as we mentioned before, the game is played at a level in which these tactical movements are averaged and included in the movement factors, they occur inside the brigade area, and not under the control of the player).
Generally (as Bob Coggins & Craig Taylor designed in the first edition of the game) an infantry unit in column formation moving through rough terrain incurs less penalty than the same brigade moving in line through clear terrain. Hence, following the spirit of the rules, we have also punished heavily units that must dress, reform or change formation. Our aim is not to change the grand tactical scope of the rules and we have followed the same precepts of the existing rules. The crucial point is that, after making our calculations, we determined that there were not sufficient empty spaces as to allow free passage. Once it was clear that the units involved needed to open ranks and then re-form, the logical conclusion was not too difficult, if we followed the spirit of the rules, about moving in formations other than column. This was the first key point we found that supported making this change.
The second supporting point was that, in essence, an occurrence that in historical battlefields was considered quite an achievement, happened many times in each side's turn while playing Napoleon's Battles. In historical accounts, units passing through other units was not common, but it happens frequently in Napoleon's Battles games. This is even more noticeable in cavalry charges and reaction movements, which would freely pass through units in Napoleon's Battles games while in the real battles these equivalent charges could never be performed for lack of space to go through (D'Erlon's attack upon the Allied ridge at Waterloo might be used as an example).
In previous editions, this represented a problem, since units could freely go everywhere, passing through friendly units (so cavalry could support many units and cover a lot of space simultaneously). This also made the games 'too perfect', with the cavalry supporting combats that were out of their line of sight or reaching them at unrealistic angles, after passing through their own lines.
Under the new rules regarding interpenetration in the 4th Edition, players are now faced with dilemmas in this regard: if cavalry support is going to be required, some space needs to be left; (or, if the player prefers a solid wall of infantry units such as D'Erlon corps did at Waterloo), friendly cavalry cannot manoeuvre easily to help them. This also prevents second line units from going through a beleaguered first line to press an attack: the player needs to make space (unless the units are elite and in the right formation to allow passage through the friendly formation). This can create mistakes and allows the enemy to punish generals that do not foresee these space issues.
As we have already mentioned, one important consequence of this interpenetration rule is its relevance to the cavalry reaction moves. Prior to this rule, cavalry units could go through a whole brigade (remember, from our calculations, without big empty spaces) and charge exactly the same distance as in clear terrain. It was clear to us that this was not correct (despite most of the cavalry units keeping their charge to a trot almost to the end) and that some penalty should be paid.
Let's suppose an average light cavalry brigade with 3/1 movement ratio while in rough terrain and 14” movement factors while in line formation. Going through an infantry in line formation would cost 9 inches. Hence, if the cavalry was 2 inches behind the line, they could attack an enemy infantry brigade 5 inches in front their own infantry (see examples). Thus, common light cavalry, mainly because of its mobility, could still move through friendly infantry.
However, if the friendly infantry were in column, the cavalry should be no more than 1” behind and could only attack a unit 3” away in front of his own infantry unit (see examples again): but we judge that it is more difficult for the cavalry if the infantry is in column because a more involved manoeuvre is necessary. Other cavalry units (heavies or with poor stats) would scarcely be able to, or even be prevented from, doing this. Examples where these kinds of units make this type of movement were historically few but could be common in Napoleon's Battles games.
With the rule as it is now, only average or good cavalry can achieve these kinds of moves, and with almost the same restrictions as if a formation change was being made. Additionally, one or both units should be in line: columns passing through columns are almost forbidden: the “impulse war” concept that encouraged formations with densely packed columns prevented such movement.
During development, we tested different proposals to address this issue, but we found the interpenetration rule eventually arrived at simple and accurate enough. Bob Coggins always preferred simple solutions over complicated solutions, and it was decided that we should find a compromise between simplicity and simulation accuracy. Playing Napoleon's Battles sometimes developed into two walls of infantry firing, with cavalry in react mode taking advantage of every disorder in every direction and from 14” inches away, thus covering a wide angle of the battlefield, but now, many of these opportunities will be lost because the cavalry must be focused close enough to the action and in a direction reducing the angle of action. This rule has been carefully tested, together with some other rules (included in the new edition) about moving artillery or making a combined arms attack which, all together, make it harder to achieve the kind of spectacular events uncommon historically but common in a Napoleon's Battles game. We have played historical scenarios that are really difficult to reproduce if these rules are not applied. Now, the side with superior cavalry can no longer take advantage of every opportunity in every direction in a radius of 14-15 inches.
We are well aware that this new rule substantially changes aspects of the game, but not the core of the rules themselves. The way players must lay out their units, if they want to achieve this kind of exploitation, is critical. Now, the player must plan ahead and leave some spaces if his second line is to advance, and some gaps must be left to allow such grand tactical movements. We perfectly understand the consequences of this but we have found it more realistic. The player that plans a crowded wall of brigades against the enemy will sleep-walk into an attrition battle, losing flexibility and lowering opportunities for with his cavalry and supporting units, to capitalize on holes that appear in the enemy line (and we think this is realistic). Players must attempt to foresee at brigade level (hence not changing the grand tactical scope of the game) where an opportunity for an all-out attack, an attack with units in reserve, or a cavalry charge could arise.
In summary, we think this simple rule, easy to use, and already covered by concepts from the rules (the rough terrain concept is not a new concept) improves the historical accuracy of the game without changing its grand tactical scope and, without slowing the game with confusing new concepts (as would be the case of paying the cost for a formation change, without a formation change being made). Sometimes, when we tended to a high accuracy level Bob Coggins reminded us that “this is a game, not a shot to the moon”. We find this rule, although possibly hard to digest by long term players (it was difficult for us to get used to the rule) makes the game more accurate and more challenging to play, which we find more enjoyable. We hope this explanation provides a logical reasoning for the change and that you give the rule an opportunity, after testing on your own. With an open mind, you will find it a challenge for you command skills, as we have done. Remember, Bob Coggins’ attitude was always: “the game is intended to be an enjoyable experience” so, if you feel you prefer not to apply this rule and go back to the ones in previous Napoleon's Battles editions you are free to do so. We recommend you to try it, but each gaming group favours slightly different playing styles, and all of them are welcome if both sides reach an agreement about the rules to be used, either optional or house rules.