The Illinois Central made its first move into streamlining with the articulated Green Diamond of 1936, which IC proudly billed as the first standard-size diesel-powered streamliner. The five-car trainset, built of Cor-Ten steel by Pullman-Standard, featured a full 1200 hp power car, a dedicated mail and baggage car, two coaches, and a diner/parlor/observation car whose kitchen was in the forward portion of the observation car but whose tables were split between the front of the parlor section and the rear of one of the coaches. All told, this combination had a capacity for 100 coach passengers and 18 parlor car (first class) passengers. I.C. placed it in service between Chicago and St. Louis, making one round trip a day on a hot 4 hour 55 minute (one way) schedule, on May 17, 1936.

The Green Diamond shared the same drawback of all articulated streamliners: lack of flexibility. The fixed consist could not easily be expanded to accommodate demand. And, as IC did not replace it before passenger car production was shut down for the war effort in 1942, the five-car trainset was forced to serve in its role for the duration. In 1947, after war's end, the original articulated Green Diamond was replaced by new equipment of more conventional construction. The old train continued to serve into 1950 as the Jackson, Mississippi-New Orleans Miss Lou, but shortly thereafter - reportedly due to recurring mechanical problems - it was scrapped.