How does defense in depth differ from a shallow defense?

• A. Defense in depth uses multiple defensive layers to slow and degrade the enemy; a shallow defense seeks quick engagement with concentrated fires but fewer layers.
• B. Defense in depth is more mobile than shallow defense.
• C. Shallow defense uses no obstacles.
• D. There is no difference between them.

Answer: (B)

Mobility and the ability to react to enemy actions differentiate a defense in depth from a shallow defense. In a defense in depth you arrange several belts at increasing distances from the enemy and keep mobile reserves that can be shifted to threatened sectors, reinforced where pressure is strongest, or used for counterattacks as the situation evolves. That flexibility requires moving forces around the battlefield and reorienting the defense as the fight unfolds, making it more mobile overall. A shallow defense, by contrast, operates along a single forward line with little depth and limited options to reshuffle forces; its emphasis is on delaying the attacker with concentrated fires at first contact, not on repositioning across a broader front. So the key difference is the defender’s ability to maneuver and reallocate forces across depth, which is why defense in depth is described as more mobile.