This from Dan McInerney:
United Airlines (B772, N782UA, ORD-NRT) 1/7/20This UA 772 made it to northern WI before turning around to come back with engine trouble. The Chicago Fire Department responded with a full ARFF assignment and escorted the plane back to the gate. As the plane turns you can see they had to shut the #2 engine down as evidenced by the lack of exhaust blur. Seen in the pictures is only a small part of the ARFF response; the Chicago Fire Department has the largest contingent of staffed ARFF vehicles and personnel of any airport in the world.