I found a video showing formation movement at around 10 seconds in. When he gives a move order, the formation moves in a narrow column facing forwards, and when it reaches destination, the formation stands still, but each soldier changes direction so that it's now a wide formation facing the enemy. What algorithms are behind this kind of movement?

It looks like the troops are moving in a certain X by Y shape facing the movement direction, and then when they reach the destination each soldier just rotates individually towards the destination.