The Force Protection Condition, or FPCON, does two things to counter terrorists or other hostile adversaries:
(1) It sets the FPCON level at Normal, Alpha, Bravo, Charlie or Delta.
Normal: Occurs when a general global threat of possible terrorist activity is possible. The minimum FPCON for U.S. Army commands is normal.
Alpha: Occurs when there is an increased general threat of possible terrorist activity against personnel or facilities, the nature and extent of the threat are unpredictable.
Bravo: Applies when an increased or more predictable threat of terrorist activity exists.
Charlie: Applies when an incident occurs or intelligence is received indicating some form of terrorist action or targeting against personnel or facilities is likely. 100% ID card check required.
Delta: Applies in the immediate area where a terrorist attack has occurred or when intelligence has been received that terrorist action against a specific location or person is imminent. 100% ID card check required.
(2) When an FPCON level is set, certain force protection measures are implemented. For example, if an Army garrison elevates to FPCON Charlie, you might see increased security measures at the gates, or even gate closures and the presence of additional security forces.
When are FPCON levels raised?
The FPCON levels are raised as a threat increases or if an attack has occurred.
For anyone who - like me - had only ever heard of "DEFCON":
https://www.army.mil/article/258076/a_community_members_guide_to_understanding_fpcon
Text below quoted from link above:
What is an FPCON?
The Force Protection Condition, or FPCON, does two things to counter terrorists or other hostile adversaries:
(1) It sets the FPCON level at Normal, Alpha, Bravo, Charlie or Delta.
Normal: Occurs when a general global threat of possible terrorist activity is possible. The minimum FPCON for U.S. Army commands is normal. Alpha: Occurs when there is an increased general threat of possible terrorist activity against personnel or facilities, the nature and extent of the threat are unpredictable.
Bravo: Applies when an increased or more predictable threat of terrorist activity exists.
Charlie: Applies when an incident occurs or intelligence is received indicating some form of terrorist action or targeting against personnel or facilities is likely. 100% ID card check required.
Delta: Applies in the immediate area where a terrorist attack has occurred or when intelligence has been received that terrorist action against a specific location or person is imminent. 100% ID card check required.
(2) When an FPCON level is set, certain force protection measures are implemented. For example, if an Army garrison elevates to FPCON Charlie, you might see increased security measures at the gates, or even gate closures and the presence of additional security forces.
When are FPCON levels raised?
The FPCON levels are raised as a threat increases or if an attack has occurred.