Firelock76- Yes that 40,000 number sounds right...thinking 100,000 was something I read years ago about total number of steam locos at the height during the '20's.
There were considerably less diesels replacing steam...certainly not one for one. Considering the savings in labour, maintainence, roundhouses, water and so forth it did not save them at all..especially in the East then the Central. Everything went to hell in a handbasket, not the diesels fault, all the positives wiped out pretty quickly.
Must have been quite the shock to see steam replaced so quickly and thoughouly as on the Erie, CNJ, New Haven, Lackawanna, Rock Island, Milwaukee, and so on.
Toronto, Hamilton and Buffalo Berkshires went into the blast furnaces 1953. The smaller roads up here dieselized real quick. CNR and CPR had an large uptick in business all through the fifities. Essentially being a "Union Pacific" and a "Santa Fe" with long transcon runs, CNR and CPR delayed a lot of scrapping becuase buisness was so good they were needed, not because diesels were not arriving on the property. In any case that gave me 7 or 8 more years of bliss. That all ended essentially in '59.