Also known as Echelon or Checkerboard deployment, the Oblique Line features units deployed behind and to the side of one another, forming a diagonal line. This diagonal line forms the basis of a few variations versatile enough for attack and defense.
The Oblique Line works on the basis of infantry units supporting each other, very much akin to the "pawn chain" seen in chess games. At first glance, the diagonal line of infantry units appears to have plenty of blind spots where the enemy can attack but, as we shall see later, there are ways for another supporting unit to counter-attack the aggressor. Therefore, it works best with a line of cheaper basic r-n-f units. The placement of one unit relative to a leading unit is such that it is far enough to the side that if the first unit gets broken, the pursuit would not clip the edge of this next unit. At the same time, this unit should not be so far that he cannot perform a supporting charge on enemies engaged with the first unit. The oblique line allows you to move forward and still maintain your counter assault options.
This chain of units can also be used as a "human shield" against enemy shooting. The reasoning behind this is that the diagonal line divides the enemy firepower (assuming it is evenly spaced out along the entire front), and placing our own firebase on either side allows us to pit our entire firepower against a portion of the enemy's.
Sicilian Dragon. The firebase on the "outside" (or "strong-side") of the diagonal line. Derived from a chess opening of the same name. This makes it difficult for enemies to advance on the firebase, having to run the gauntlet of covering units.
Meat Shield. Similar formation, but with the firebase now on the "inside" (or "weak-side") of the diagonal. The firebase can now work on shooting enemies advancing down the weak-side, while the rest of the army advances to contact the enemy.
Note that in these diagrams, there is always a fast heavy hitting unit "inside" the line. This unit functions as a "Lock" for the infantry "chain", and is a vital part of the defense. This unit is the heavy protection unit that keeps the hinge alive, and can also act as the counter assault unit. It's generally deployed behind the chain so the chain does not ever have to turn around.
The diagonal line is able to put up a robust response to a variety of opponent strategies to break the chain. The concentration of centrally located mobs denies the center of the board while the fire base whittles down the opponent. Any attempt to break the chain results in a heavy counter assault. This formation is especially useful for taking objectives, as it is mobile, protects the fire base and can easily support a battle for a central point.
The major weakness is if your opponent has unit strong enough to roll your line. They could potentially massacre one squad after another as it eats it's way down you army. Also, if the enemy manages to push a few units "inside" the line, stronger than the Lock can handle, part of the line must turn inwards to provide support.
Mechanized armies can deploy in oblique lines with much success. It allows them to maintain better firing arms than lines abreast, and it funnels opponents into massed fire power. Lines abreast are very vulnerable to flanking and pincer attacks and deal very poorly if flanked. A mechanized in an oblique line cannot be flanked as they can always make a 90 degree turn to cover the flank and rear.
The Oblique Line is a very usable and interesting formation to add to one's arsenal, especially if one fields a balanced army and likes tactical fireworks. It works well with all hth, counter assault and shooting tactics and allows you to mix and match tactical situations.