As an aside, the UK had a similar system back before our 'UK Threat levels' called the 'BIKINI States'. Honestly, I prefer the BIKINI states over this new fangled system which doesn't seem to move much beyond 'Severe'.
Bikini States:
WHITE - Situation stable, normal procedures apply.
BLACK - There has been an assessment of a possibility of an attack, but no defined target, it could also mean civil unrest meaning that safety cannot be guaranteed.
BLACK SPECIAL - There is an increased likelihood of attack but no defined target, can also mean potential terrorist threat.
AMBER - There has been information received and there is a substantial threat to government targets, it can also mean high alert which could mean a
transition to war.
RED - Information has been received about an attack on a specific target, it can also mean that the UK is at war, especially if there is the risk of a nuclear strike.
NATO itself had a system-wide 'counter-surprise' alert level which went:
ORANGE - Triggered by intelligence reports suggesting that the enemy are preparing to launch an attack within 36 hours, NATO forces go to a high state of operational readiness, Communications networks, War HQs and Command and Recon manned, forces dispersed to operational locations.
SCARLET - Enemy attack expected within minutes, deployment as Orange level as permitted, SAM and AAA weapons manned, aircraft awaiting orders.
