[u]ORION[/u] - Took volunteers and gave them relatively trivial augmentations compared to the later programs. [u]SPARTAN-II[/u] - Members were conscripted at the age of six and indoctrinated. Upon reaching the age of 14 were augmented with highly invasive surgery that maimed or killed roughly half of the conscripts. The results though were extraordinary, and beyond what was expected. [u]SPARTAN-III[/u] - Orphaned children from the ages of 4 to 7 were manipulated to join with the promise of revenge against those who killed their families. They received augmentations roughly at the age of 12. They were non-invasive and chemically induced. Survival rate was 100%. [u]SPARTAN-IV[/u] - Members are chosen on a volunteer basis. Age doesn't matter as long as their genetics allow for augmentations. Augmentations involve entire organ replacements as well as an induced second puberty for enhanced growth.

Spartan-II's where kidnapped at 6 Spartan-III's varied in age as they recruited orphans from glassed colonies and offered them a chance at revenge against the covies. Sartan-IV's are from all other military branches that pass the requirements test get some augments and armour. A fair few are ex-ODST's As for the Spartan-1's they where regular soldiers recruited into the Orion project and tested on to try and create super soldiers not sure how many there where or how successful they where but Sgt.Johnson was from the S-1 programme.