maybe it wasn't in contact harvest... haven't read that one in a while. but it is stated several places.
And Although Orion was its original name it did late become officially called Spartan I. and it has many more members than SII, but less than SIII. in order of combat strength of individuals it goes SII>SIII>SI but thats mostly because of the lack of potency of the augments used on SI's... SI's were better trained that SIII's and had a lot more experience.
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