I know there's a lot of debate around this rule, but a friend pointed out to me that the rule comes from Warhammer Ancient Battles, I went back and checked and he's right. There's a lot of things from WAB that have made it into the old world, in fact I would argue it's perhaps the biggest single influence on TOW in terms of editions, even more so than 6th. There are also key diagrams that have been copied exactly from that book (manoeuvreing while charging, redress the ranks etc.) as well as mechanics such as marching column (called fast march in WAB).
The "Drilled" rule in Warhammer Ancient Battles:
As you can see the concept is far more clearly explained in the WAB book and is actually significantly more powerful in WAB than TOW with the ability to turn and not just redress ranks.
Going by this interpretation of being able to redress the ranks before charging, I was thinking about what are the optimal units sizes and formations for our Drilled units in TOW? Combined with the mechanic of your whole front rank being able to attack, it makes things a little interesting.
Marching Column's rules state:
It's a little unclear however does the rear rank have to be complete (i.e. 4 or 5 models) or as long as there is 1 model in the rear rank making the formation deeper than it is wide is that sufficient?A unit that is deeper than it is wide (i.e., that has more models per file than per rank, as shown in Fig 101.2) is said to be in Marching Column. A Marching Column cannot claim a Rank Bonus and cannot make a charge move, but may triple its Movement characteristic when Marching.
Sample unit sizes for units trying to make use of the marching column ---> redress into close order ---> charge mechanic:
A)
Unit of 7 deploys 2 wide, can redress in to a single line of 7. Perfect for Dragon Princes, maybe Swordmaster darts.
B)
Unit of 13 deploys 3 wide, can redress into a line of 8 with 5 in the second rank for +1 rank bonus. Seems ideal for Swordmasters.
C)
Unit of 17 deploys 4 wide, can redress into a line of 9 wide with + 1 rank bonus, maybe better for Phoenix Guard.
Please note: this sample is only valid if marching columns can have an incomplete rank
D)
Unit of 22 deploys 4 wide, can redress into a line of 9 with +2 rank bonus (heavy infantry), ideal for Phoenix guard.
Please note: increase to 23 to gain +2 rank bonus with regular infantry
I flicked through the other lists, and the only cavalry units in the game that have or have access to Drilled are:
Dragon Princes
Empire Knights
Empire Inner Circle Knights
Blood Knights
Cold One Riders (Lizardmen)
Chosen Chaos Knights
Dragon Princes are the only of these units to have M8, giving them a 24" move in marching column vs 21" for the rest. This may well be a key difference in how they can be used, however it's worth bearing this in mind when you come across the aforementioned units on the tabletop; ensure they cannot march onto your flank and out of charge arc.
People may argue that drilled can also be used in conjunction with countercharge to avoid being caught in marching column, but as this in the enemy turn and not your move phase, I expect that this will not be allowed.
I hope this is useful to others and encourages some tactical discussion. One thing worth considering with these optimisations however is how many casualties can you sustain before you are "knocked" out of marching column, it depends a little on the interpretation how many models need to be in the rear rank. In WAB the rule is a bit more simple, the unit simply has to be a maximum of 3 models wide, which perhaps would have been better.