"Halo 4: I Get a Woman!" - Sgt. Mjr. A.J. Johnson, RIP

[Cortexian]

The only issue you saw? Lol.

But no, actually. Navy addresses its MCPOs as Master Chief [last name]. With their names still classified, that's appropriate.

Since when have you ever heard or seen John's last name used in the canon after he became a fully augmented Spartan II?

He always responds with his full official name of "Master Chief Petty Officer, John 117". For all intents and purposes, 117 is his last name since the whole Spartan program dehumanized the Spartan candidates.