It pays to be first.

American railroads ran on steam locomotives thruout World War II.  Immediately after the war they began to convert to diesel locomotives.  By 1957, a mere 12 years, diesel conversion was mostly done.  Only the diehard Norfolk and Western was still running steam.  We are talking about replacing every locomotive in service in a mere 12 years.  That is one heck of a lot of locomotives.
   And, one company, the Electro Motive Division of General Motors gained the bulk of this business.  Other locomotive builders, Baldwin, ALCO, Fairbanks Morse, Ingersoll Rand, and General Electric  were driven from the market.  EMD sold 9 out of 10 locomotives in the early post war years.
   What gave EMD the edge?  Back before the war, EMD had been working hard to grow self propelled passenger rail cars into real road freight locomotives.  In 1939, on the eve of war, EMD put the 1300 horsepower FT freighter on the market.  There had been a few switch locomotives, of 600 horsepower or such, and low speed trucks built, but the FT was the first unit with enough power to move a big train at road speed.  Not only that, but the 1300 horsepower units could be coupled together, to form four unit lashups with 5200 horsepower.  That was enough to move anything, over any kind of mountain.  EMD managed to build and sell a few dozen units before WWII.
   When America joined WWII, the government set up the War Production Board to mobilize American industry for the existential struggle.  The new high tech diesel engines were needed for submarines, to power air and army bases, and dozens of other crucial tasks.  War Production told the railroads they would have to make do with the traditional steam locomotives, there was a war on, the the diesels were needed to fight it.  The only diesel railroad locomotives running were the few dozen that EMD had put on the rails.  They ran thruout the war, and those teething troubles that new machines are subject to were discovered and fixed before the war ended.
   So, when the post war locomotive boom began, EMD was the only company with a tested, debugged, and reliable design.  The also rans had to debug their new products, at the customers expense.  The customers noticed, and flocked to the reliable EMD product.  Which gave EMD the entire North American locomotive market for decades. 
It pays to be first.