John Cochrane writes,

I ran across a fascinating article, “A Post-Mortem on Transition Predictions of National Product,” in the 1946 Journal of Political Economy, by Lawrence Klein. Klein, who would go on to create the main macroeconomic forecasting models and a Nobel Prize, was confronting one of the first great failures of Keynesian economics:

We all recall clearly the headlines in last Autumn’s press, declaring that “Government economists predict 8 million unemployed by 1946.” …We now find ourselves in the first half of 1946 with about three million unemployed and facing one of the greatest inflationary pressures that we have ever experienced. The economists who were warning us of a deflationary danger during the early months of the postwar transition period should have been stressing precisely opposite economic policy

As I have pointed out, 1946 is a striking instance of the predictions of Keynesian economics being way off. Recall David Henderson on what Paul Samuelson predicted.

[UPDATE: Russ Roberts unearths an even more damning article, from the 1947 JPE, by W.S. Woytinksy.]