Missouri Pacific power on Poplar Bluff run.

[yankee flyer]

 Hi All 

I had an uncle that started firing on the MoPac during "WW2" and retired as an engineer. I vaguely remember when he took the engineering test on steam and when he ran Diesel but I can't remember when MoPac switched over. His run was from St. Louis to Poplar Bluff and back. Any help appreciated.
Good day.

Lee