What is the command given to march to the flank?

The command to march to the flank is given as "BY THE LEFT FLANK, MARCH" or "BY THE RIGHT FLANK, MARCH," depending on the direction of the movement. The use of "BY" in these commands indicates that the unit will pivot on the foot closest to the direction of the turn, allowing for smooth, coordinated movement.

In the context of the question, the command "BY THE LEFT FLANK, MARCH" specifically instructs the unit to face left and march while maintaining alignment. Similarly, "BY THE RIGHT FLANK, MARCH" would indicate a right turn. The phrasing directly relates to how commands are structured in military drill, ensuring clarity in command and execution.

Thus, one can see that the correct phrasing includes "BY" as a directed method of turning to a specific flank while marching, which emphasizes the transition and marching direction required.