Final answer:
A "break glass in case of emergency" OPSEC plan indicates the need for relief in place, employing tools like 24-hour drone surveillance to monitor and quickly respond to threats, while addressing communication barriers about the operation's potential collapse.
Step-by-step explanation:
The OPSEC plan that usually indicates that a relief in place is necessary is one that acts as a "break glass in case of emergency" safeguard. This form of plan is set in motion when immediate action is required due to unforeseen circumstances or threats, such as those related to security breaches or a critical change in operational conditions. Advanced monitoring techniques, like 24-hour drone surveillance, might be essential for maintaining security and identifying when such a relief in place must be initiated.
Additionally, the need to address communication barriers about potential operational collapse illustrates that contingency planning is critical for effective response during emergencies, reflecting concerns raised by U.S. military strategists over major issues such as a diminishing petroleum supply.