The COW (Clinic on Wheels) is a converted van that can be used as an ambulance or as a mobile clinic. It was cobbled together from a stolen DocWagon ambulance, an old van and supplies from the clinic. For a while, it was the only clinic the Nest had.
There is room enough to treat two patients at the same time and it has sufficient gear and supplies for emergency operations, as Growler was the first to test this when his liver failed while the Nest had been taken over by the Picas. It's usually parked at the Nest to handle anything the san container can't handle.