FPCON Delta, the highest and most protective level, limits installation access to mission-essential personnel and other personnel as determined by the commander.
What is the most increased force protection level for a base/installation
The highest level of readiness under the system is Delta, and it is unique compared to the other levels in that Delta is the only level that may refer to a specific known threat.
What is Delta level of protection?
Force Protection Conditions DELTA–This condition 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 likely. Normally, this Force Protection Conditions is declared as a localized condition.