Excuse me, that was an error on my part; careless. Not very relevant, but well done in any case!
ETA- My quote related to "the amount", not the proportion, which, according to your figures, has only been beaten once, though I'm sure there are more examples.
You seem to have neglected, for whatever reason, to have adjusted for inflation. Further, direct comparisons of defense budgets from one era to another are highly problematic. With the all-volunteer army, personnel are individually much more expensive, and weapon system costs have skyrocketed far above the overall rate of inflation. So an argument can be made that the US gets less defense today, dollar-for-(adjusted) dollar, than in earlier times. Further, the United States, and the world at large, have much greater populations than during World War II. Finally, because the US economy has grown so much, even since the Vietnam War, the country simply has much more money to spend for everything, including defense. In other words, if your income triples, you may suddenly start driving a much nicer car, which might have seemed extravagant at your old income level, but is not a major financial drain for you and your new money.
US military spending, 1943 $526 (37.0%)
US military spending, 1944 $684 (37.8%)
US military spending, 1945 $775 (37.5%)
US military spending, 1946 $406 (19.2%)
US military spending, 1952 $397 (13.2%)
US military spending, 1953 $416 (14.2%)
US military spending, 1967 $383 (8.8%)
US military spending, 1968 $420 (9.4%)
US military spending, 1969 $400 (8.7%)
US military spending, 1989 $399 (5.6%)
US military spending, 2003 $405 (3.7%)
Billions of 2000 dollars (percent of Gross Domestic Product)
Source: Office of Management and Budget
Based on the above, your contention that the FY 2003 defense budget was somehow "unprecedented," or at least excessive, is rejected.