Inverted wedge
The inverted wedge is a military formation resembling a "V" or inverted triangle, and is sometimes known as a "V-formation".  In the inverted wedge, two units advance abreast of each other, and a third  unit follows behind and between the two, in reserve.  It is roughly the reverse of the flying wedge formation.

The inverted wedge is particularly effective for encircling an enemy force, village, or other strategic objective. The leading units envelop the objective to the right and left, while the remaining unit is free to search, attack, or support one or both of the leading units as the situation requires. Arguably the most famous use of the inverted wedge was by Hannibal at the Battle of Cannae, where he surrounded the numerically superior Roman force. 

The inverted wedge formation is used ceremonially by cadets at the United States Air Force Academy each year at the acceptance parade in the fall, when the new fourth-class cadets (freshmen) join the Cadet Wing.  The formation is reversed at the spring's graduation parade, when the soon-to-be commissioned first-class cadets (seniors) leave the Cadet Wing in the flying wedge formation.