I dug up some numbers from this document, which is chock-full of interesting numbers. Worth downloading and browsing through.

I hope I read the numbers off right:

From Table 4.2: In 1973, Defense spending was 30.5 percent of the Federal budget. Interestingly, this was a maximum. It dropped to the 20 percent range, and continued to head down to where it is now, floating in the 16 percent range. Remember, this is a percent of the budget, not the amount of spending.

From Table 6.1:

Defense spending in regular dollars in 1973: 76.6 billion. 2004: about $400 billion (the chart is probably not up to date on this.)

Defense spending in constant (1996) dollars in 1973: 255.3 billion. 2004: 335.5 billion

As a percentage of GDP in 1973: 5.9 percent. 2004: 3.5 percent.

Remember, 1973 was the height of the Cold War.

Here's something to think about. In 1973, the Federal budget was only 42 percent of what it is now. In constant 1996 dollars, adjusted for inflation. Have a cup of coffee and think about that a while.