An echelon formation is a military formation in which members are arranged diagonally. Each member is stationed behind and to the right (a 'right echelon'), or behind and to the left ('left echelon'), of the member ahead. The name of the formation comes from the French word échelle, meaning ladder, which describes the staircase effect that this formation has when viewed from above.
Use of the formation dates back to ancient infantry and cavalry warfare when attempting to flank an enemy or to break one wing with overwhelming numbers. One of the earliest uses was at the Battle of Leuctra when the Thebans attacked the Spartan right with a column 48 men deep while their weaker center and right were refused. The echelon formation was also used by Frederick II of Prussia.
The tactic persists up to the present day, where it is regularly employed by all branches of the modern armed forces. Tactically, echelon formations are used because of the excellent range of vision offered to each participant in the formation. In particular, it is commonly employed by armored cavalry because of the large, overlapping fields of fire that it gives to each tank in the formation, and by combat aircraft, where the close, streamlined flight formation can allow the planes to dramatically reduce fuel consumption by "surfing" the updraft created by the wingtip vortices of the aircraft ahead.
"Echeloning" is the name of a tactic in use by the United Kingdom's Armed forces, mainly the Infantry. It consists of using a Company to attack a set of positions. Once the first platoon in the company has reached its limit of exploitation (either ammunition has been expended, fatigue has become high, or casualties are mounting) another platoon "echelons through" it, to continue onto the next position. The tactic is similar to "leap-frogging"
Echelon formations are also commonly used by civic, or riot police to move crowds either to the left or right.
In geology an echelon formation is a set of short linear features that overlap or are staggered in a line that runs obliquely to the strike of the individual features. Echelon faults are an example of this.
In mathematics, it refers to a kind of matrix where the non-zero elements are shaped in an echelon-like manner.
In road bicycle racing, an echelon formation is that of a diagonal line of cyclists, in which the front cyclist makes the main effort, shielding the rest of the pack from the wind (which meets the cyclists side on). The front cyclist usually peels off after a short period of time, and joins onto the back of the line, whereby the next cyclist then takes the power of the wind, so the pack rotates, allowing for everyone to get an equal share of the work. This formation is commonly used in breakaways or team time trials.