In the bad old days of the Cold War – back when everybody planned on ending the world, but (unlike today) nobody actually meant anything by it – aircraft carriers entering port at Subic Bay, the Republic of the Philippines would launch a two-ship of combat air patrol, or CAP prior to entering harbor.
The PI is an archipelagic nation, meaning that while there are certain clearly defined constraints placed on surface ship navigation – running aground not least – there are some additional oddities in international law that apply to overflight of what would ordinarily be sovereign national airspace: This results in two codicils within the body of law, the first a “right of archipelagic passage” and a second, more restricted right, the sometimes euphemistically labeled “right of innocent passage.”
Through ancient custom and the international law of the sea (which are nearly the same thing), countries have the right to the sovereign control of their airspace and seas extending 12 nautical miles beyond their terrestrial limit, measured at low tide.
But a problem arises if archipelagic nations – clusters of islands scattered about hither and yon – attempt to enforce control of their separate islands’ interlocking 12nm limits: Vast swathes of the ocean sea would be non-navigable to foreign ships without prior permission from the archipelagic sovereign. Archipelagic and innocent passage are therefore designed to permit transit through the archipelagic seas so long as that passage is “for the sole purpose of continuous, expeditious, and unobstructed transit in the normal mode of operations.”
Which could mean different things to different people. To a US aircraft carrier heading into Subic for some well-deserved liberty ashore it meant wrapping the deck nice and tidy and making herself pretty for the pier. But for them godless communists out there yonder it meant a chance to “innocently” overfly an imperialist running dog capitalist aircraft carrier what with its drawers down and napping, like – on account of the lack of air cover that was in it.
Which would never do, because it was written somewhere in the bible – Old Testament, I believe – that any battle group commander who allowed his flagship to be overflown by a Tupolev that wasn’t being bird dogged by one of his own fighters would spend the eternity in hell, roasting over a slow fire with a spit up his arse. I’m nearly sure it was in the bible because for all those Cold War years they put the rest of us through hell to prevent it, but anyways.
So if you couldn’t be overflown, and you couldn’t develop a plan for alert fighters because you couldn’t rely on having the sea space necessary to turn into the wind to launch ‘em, what you could do was launch a gate guard of CAP before entering territorial waters and then tank the hell out of ‘em until the ship entered the harbor.