Which of the following is NOT a principle of machine gun employment?

Isolation is not considered a principle of machine gun employment. In the context of machine gun tactics, the principles revolve around maximizing the effectiveness and survivability of the weapon system while delivering effective fire support.

Defilade refers to using terrain features to protect the machine gun from enemy fire, allowing the weapon to engage targets without being directly exposed. This is crucial for ensuring the crew's safety and maintaining operational effectiveness.

Economy of fires emphasizes the efficient use of firepower, allowing for maximum impact with minimal expenditure of ammunition and personnel resources. By concentrating fire where it is most needed, forces can achieve significant effects while preserving their capabilities.

Protection involves measures to safeguard both the machine gun and its crew from enemy actions, including the use of cover, concealment, and tactical positioning.

In contrast, isolation does not align with these principles. While it may refer to keeping a machine gun crew or position separate from other units for operational reasons, it is not a tactical principle focused on enhancing the utility or survivability of machine gun fire.