The Procrustean planet was an otherwise unnamed planet located in the Organian Treaty Zone within the galaxy's Alpha or Beta Quadrants.
History and specifics[]
It had once been inhabited by an advanced civilization, nicknamed the Procrusteans, but by the 23rd century it was a dead world.
In 2270, the Federation starship USS Enterprise received an automated transmission from the world, promising visitors scientific advances. However, a landing party found only an abandoned alien city, with a plaza containing several debauched pleasure palaces. Suddenly a planet-wide force field snared the starship and knocked out the landing party. Machines carried off the people. Each awoke to find their sex transposed, or an additional chromosome added, and a transporter began beaming down and transposing more of the crew.
Kang's Klingon battlecruiser decloaked, and he claimed this to be a new weapon. Actually, the Klingons arrived two weeks earlier and were similarly trapped. By the time the ships were able to break orbit, all of the Klingon crew and 66 of the Starfleet crew had been affected.
One month later, with Admiral James Komack's approval, Captain James T. Kirk took the Enterprise back to the planet, carrying a crew only of those who'd been changed. Kirk hypothesized that the machines wouldn't realize it was the same ship as before, and would re-swap everyone's sexes. It did, for the most part, as well as for Kang's crew. (TOS - The New Voyages 2 short story: "The Procrustean Petard")