Final answer:
Optimum length of command for Field Grade level refers to a manageable stretch of control that ensures troop effectiveness without overextension. Overextended commands with forced marches can lead to command vulnerabilities and potential capture by the enemy.
Step-by-step explanation:
The optimum length of command for a Field Grade level is not explicitly stated in the given reference material. However, the reference suggests that overextending forces with forced marches and without rest, aiming to cover excessive distances quickly for tactical advantage, can compromise the integrity of the command. It implies that a command should be at a manageable length to maintain control over the forces and ensure their readiness for engagement.
For instance, if commanders push their divisions to march continuously day and night, and cover double the usual distance, the troops may become exhausted and more vulnerable to enemy capture, as stated "the leaders of all your three divisions will fall into the hands of the enemy". Therefore, the optimum length of command must be balanced to maintain troop effectiveness and prevent leadership from becoming overextended and falling prey to the enemy.