Oahu (O'ahu) is an island, in the north-central Pacific Ocean - one of the eight principal Hawai'ian Islands - and a location in the episode Danger At Ocean Deep.
After the island is hit by a typhoon (hurricane), putting hospital patients there in peril, the distress call goes out: "Calling International Rescue..."
Oahu Rescue: "Requiring immediate action..."Edit
From Thunderbird 5, John Tracy relays the emergency call to Tracy Island. Speed is essential - and Scott Tracy is immediately dispatched, aboard Thunderbird 1. After receiving updated information from John, Scott asks for Thunderbird 2 with double crew and Pod 3; and Virgil and Gordon Tracy get the call to go...
...and that's about as far as anybody gets, as contact with TB1 is suddenly lost. TB2 can't get through to base, either; and when Thunderbird 5 also goes silent, International Rescue finds itself left blind and deaf...and, with a major rescue operation underway!
Aftermath: "Boy, that was close!" Edit
With communications still disrupted, TB1 manages to land safely back at base. A very muddy-looking Scott reappears in the Tracy Villa lounge, and relates details of the rescue: they'd managed to shore up the hospital walls with hydrostats, but not before the isolation ward collapsed. Luckily, no cases had been in that ward at the time, and thus no casualties.
He also reports that, although Thunderbirds 1 and 2 were able to talk to each other (indicating short-range transmissions were nominal), neither could make contact with TB5, or elsewhere. And he adds that Virgil and Gordon are "even muddier than me!"
- This rescue is noteworthy in that it occurs entirely off-screen.