When in the course of human events, a force must force a valley or pass, the walls of the valley have themselves ridges and gullies (smaller valleys) at a sharp angle to the valley traversed. The movement up the main valley then can face direct fires from the head of the valley flanking fires from high ground down the gullies and along the ridges down into the main valley. Thus fingers have fingers and valleys of their own and are significant on fires and movement of successive levels of command.
There are corps sized valleys and squad sized valleys of a smaller scale. Those of us trained in ground combat in the not too distant past focused on hills defined by the size of the force to be deployed. There were squad sized hills for squad training, platoon sized hills to train platoons, and so forth. This was goose egg centric with successive positions designated by the appropriate goose egg, be it squad or division.
Avenues of approach were connected swatches of white space on a map leading to the appropriate goose egg which was fine so long as the tanks stayed in the white, and infantry in the green. In Germany I lead a mechanized infantry platoon in large unit field exercises through the network of logging trails that define German woods. In Vietnam, the unit I was attached with had little difficulty in busting jungle in pursuit of foot mobile Viet Cong.
During the many years of participating in training rotated annually from individual to division level exercises, I had to wait until the big exercises to train my unit in learning to fight on fingers, valleys, passes as well as hills and to maneuver both across and with the grain. Formal training at successive levels of command sought terrain that fit the preferred plan of maneuver, be it a squad maneuver left or a mobile defense with strength in reserve to delivery a devastating counter attack in a assumed penetration. Assumed!
In combat operations involving a lot of movement over unfamiliar terrain, one must have something more than goose eggs and white spaces to constantly update actions on contact which could occur before this sentence ends.
Our Civil War gives some fine examples. First at hand is the Battle of Little Round Top at Gettysburg on July 2, 1863. The day before saw the Army of Northern Virginia had nearly flanked the Union position on Missionary Ridge around Culp’s Hill. They would try again while Longstreet would launch his Corps against the southern end of Missionary Ridge with Hood leading the attack against the exposed flank of Meade’s line.
A few quick thinking Union officers saw the importance of Little Round Top at southern end of Missionary Ridge with provided clear fields of fire across the front of Missionary Ridge, and which, due to it’s concave slope facing the Confederates, provided clear plunging fields of fire well past the base of the hill, and grazing fields of fire on it’s southern slopes. The shape of this hill provided nearly 270 degrees of coverage from a small force firing from a centrally located small area/
Colonel Strong Vincent, MG Gouverneur Morris, and Colonel Joshua L Chamberlain, quickly saw the advantages of Little Round Top and moved troops on their own initiative to stop the Confederate attack in one of the most memorable battles of the War.
Later, at Appomatox Court House, Colonel Chamberlain would order his men to present arms to defeated Confederate forces at the surrender in the effort to pave the way for a just peace. A peace shattered by John Wilkes Booth and the vengeance of the Reconstruction.