A man in the Air Force is grabbed and put on a 'train' with dozens of young thin teenage girls (except for one chunky girl who is grabbed by mistake) and sent to an underground bunker to ride out the end of the world. He develops a love affair with the chunky girl and encourages all the girls to have sex with each other by overriding the 'censure' monitoring software installed by the government. I read the story here or on asstr not sure which. Thanks