I was told that WP wanted to buy articulated steam locos to expedite wartime traffic, but the WPB allocated FTs instead, citing bad water and a shortage of maintainers on the WP.
Somewhere around 1956 I toured a destroyer escort powered by diesel-electric drive - 4 General Motors engines driving 2 shafts. That was one ABBA lashup that couldn't be powered in 1943...
N&W wasn't put out of the steam business by the loss of the major builders. What killed them was the lack of availability of rellatively minor parts from small suppliers who either curled up and died or moved on to more profitable lines. When the Pilliod Corporation stopped making parts for Baker valve gear...
A little-noted facet of rail dieselization was the sudden availability of al those 'war service' Machinist's Mates who started looking for jobs when the Navy all but imploded at the end of hostilities. Hired on at no seniority pay, and with no loyalty to the Brotherhoods...
The major steam builders sat back and waited for their customers to order custom-designed locos that exactly fit their requirements - in small batches. EMD, using sales tactics that would make a used car dealer blush, marketed a standardized, mass-produced product with a limited number of relatively inexpensive options. Rather like Rolls Royce versus Chevrolet - in a market looking to cut costs.
Last, but hardly least, there had been a steady stream of propaganda about all the wonderful new things that would come with peacetime. It was, "Out with the old, in with the new," in the entire society, not just the rail industry. Steam was old, dirty and expensive. Diesels were new, clean and wore pretty paint jobs...
Chuck (Modeling Central Japan in September, 1964)