Interestingly, nobody has calculated the share of the US gold reserves in the world gold reserves between 1913 and 1945. I researched the Federal Reserve Bulletin and came across the following series. I have visualized the historical gold reserve data from 1913 to 1945 based on Federal Reserve Bulletins. The chart tracks the U.S. percentage share, showing how the U.S. went from holding about 26% of global gold in 1913 to a peak of nearly 67.5% in 1940.
Source:
1913-1925 data from FEDERAL RESERVE BULLETIN, DECEMBER, 1929, Page:271
1926 data from FEDERAL RESERVE BULLETIN, APRIL, 1929, Page:263
1927-1929 data from FEDERAL RESERVE BULLETIN, APRIL, 1926, Page:800
1913-1940 data from FEDERAL RESERVE BULLETIN, September, 1940, Page:1006-1007
1940-1945 data from FEDERAL RESERVE BULLETIN, December, 1945, Page:1257