Got the “Operation Completion” achievement (Halo 4: Complete a Spartan Ops mission.) when I started a spartan ops mission, but quit immediately after it started (I forgot to configure my load outs).
On a somewhat related note, you really should be able to configure load outs in-game Halo 4. (I swear I remember being able to do that in the 360 version.) Otherwise I have to do it next game/quit out & restart.