This requires the Insurgency DLC pack.
Simply beat the Portland, ME map on any difficulty. Since the Team Congratz achievement requires you to beat all the maps from the DLC pack on realistic, you might as well do this on realistic to work towards that achievement as well.
I believe this can be done in either Hunter or Last Stand, but given that Hunter is *MUCH* easier, I'd recommend going with that mode (that's what I did).
You can be detected as many times as you want, you can retry as many times as you want, you just simply have to get through all areas.
One more thing to note: in spite of the achievement description reading "CO-OP", all the achievements from the DLC pack can be done in local solo Hunter play.