I think just about every Halo fan lost their shit when they saw the newest ship, the Infinity, wreck a Covenant cruiser like it was nothing, and it was at that point that I thought to myself, ‘Holy crap, the UNSC isn’t taking any alien shit now.’
Similar to the Ancient Spartans of Greece, the candadites for the Spartan Project were selected at an early age (6). Yet unlike traditional Spartan children who were surrendered for the good of the sate, the candadites were kidnapped by the state. They then trained the children in warfare and tactics until later augmentation. These subjects were mechanically augmented in order to fully integrate with the power armour they would later aquire. Their power armour dubed MJOLNIR (the Viking God Thors Hammer) increased the already mechanically augmented strenghth of the Spartan II, offering them superior protection, limited shielding, and even the ability to survive limited exposure to the void of space.
Spartans never die, the Spartan II were the UNSC’s greatest weapons in the war against the covenent and the victories of these super soldiers greatly bulstered the moral of UNSC forces. With only 33 Spartan II total each was a treasure, to keep moral up, and reinforce the apearence of invinsibility any Spartan killed in action was declaired Missing in Action.