Starting torque is certainly a factor in diesel electric locomotives but another reason is that building a torque converter capable of managing 4000+ hp is expensive and they tend to be somewhat problematic when subjected to North American railroad service. Nevertheless, it was done in the '60s by, you guessed it, the Germans.

At the time, Krause-Maffei ML4000s diesel-hydraulics were the highest horsepower, single prime mover locomotives being built. Lower HP diesel hydraulic units are still used all over Europe.

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