I'm not sure how many of you obsessively collect achievements like I do, but here's the achievement list, barring the secret achievements. Hm... looks like the difficulties will be Normal, Veteran, and Professional. It looks like there's only going to be six missions (Witness regarding the prologue with Birkin and HUNK).
That said, I'm wondering, since the listed achievements specify the "USS Campaign", with no mention of Spec Ops, I'm wondering if they're going to be playable in an unlockable, secret campaign. There's ten achievements related to the USS Campaign (Six for missions, plus one each for completing the game on veteran and professional, plus one for S-ranking, plus one for S-ranking on veteran or professional). There's ten hidden achievements; so... could they belong to a similarly-long Spec-Ops campaign?