Not 400 canditades made it through the Spartan II augmentation program. Around thirty three I think made it through still combat capable, about a dozen others survived but were no longer able to physically perform their duty. Those lost were ejected into space with the Chief's and the squad leader John standing at attention. John to this day still does not understand whether the lives of his men were wasted or spent.
It's my knowledge that approximately half of the children died during the augmentations, so there were seventy five children taken in total. The augmentations took place on an orbital medical facility orbiting Reach.
There is always speculation that there were more candidates, and that is true. 150 in total, but they only had the funding for half of them, seventy five. Only seventy five canditates were taken for the project.
Note the John and his comrades are NOT the first Spartans, hence SPARTAN II. The original project was started in 2491 as part of the ORION program. I dont know much about the original Spartans, but logically they were sucessful enough to warrant a second more refined program.
Sorry Wolf. It was never as much as four hundred.