iammitchell:

Once the covenant glassed Harvest, the Spartan-II's were taken to a military facilty and given the MJOLNIR mk III armor. It had no shields, however it improved their reflexes and strength and speed almost as drastically as the augmentation had. The Spartan-II's were the only humans capable of controlling the armor due to this (as it describes an ODST attempting to use it being torn apart). The Mark III armor had no shield. When the Spartan-II's were sent onto their mission to capture a prophet, Dr Halsey gave them the Mark IV armor which, using captured covenant technology, had a shield system, which makes the Halo's we all know and love. I won't tell you anymore in case anyone trying to prove people here wrong hasn't read the book yet...

 Spartan-III's, well, i can't really say much here because i can't get a hold of Ghosts of Onyx yet, so i'll let someone else *cough UNSC AI #23 cough*

Hold on, I'm pretty sure that the MJOLNIR without the shields is the Mark IV. Master Chief uses the Mark V in Halo: Combat Evolved, I'm almost positive this is right (haven' read the books in about 2 years, and currently reading GoO) because in the begging of Halo 2 Master Sgt. Gunns says:  "Well, I guess it was all obsolete, anyway. Your new suit's a Mark VI, just came up from Songnam this morning." which means its highly unlikely that Master Chief was wearing Mark IV during Halo: Combat Evolved, because Master Chief didn't get another amor upgrade until Halo 2.  Also in the Halo Graphic Novel the section titled Armor Testing in the second box some one says: "Preparing test and catalogue of A-12-121 MJOLNIR Mark VI Armor."  Also on the description page of the section it says: " that dear of Ma-117 didn't just knit him that suit og Mark V MJOLNIR Assualt Armor when he was a wee bairn."  So I think that the Armor that the SPARTAN-I's are wearing is the Mark III MJOLNIR Armor.