Wow. But, didn’t they do it by selling bonds (as much as they could)?
About half the cost of the war was financed by war bonds, most of which were bought by corporations, the rest by individuals. But there was still plenty of other government debt in the market and that's what the Fed was buying.
Another bit of related trivia is that 1946 had the highest rate of inflation in the twentieth century. That's the year that war time price controls were lifted.