The archillies armor can only be obtained by joining a company. You and other spartan companies have to work hard and complete commendations. Its not that easy to do them unless you have a good amount of people completing the commendations. SO, WHY IN THE HELL OF THE WORLD IS THE ARMOR ULTRA RARE?!?!?! The armor should be legendary or Ultra Legendary!!
Why does it matter?
I think you mean achilles