Since WWII. I have four uncles who were flyboys in the Army and Navy Air Force in WWII, and they all were given "pep pills"(amphetamine) before missions to sharpen focus, quicken reflexes, battle fatigue, etc. My step father was a career combat pilot from WWII through Vietnam and relates that such drugs, along with many others, were easily available, and their use unofficially encouraged.
Modern day use is still common, and even encouraged.
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http://www.csmonitor.com/2002/0809/p01s04-usmi.html>
Perhaps you remember the friendly fire incident in Afghanistan a couple of years ago that involved speed: Jan 2, 2003 WASHINGTON (Reuters) - Two U.S. F-16 pilots charged with manslaughter in the April "friendly fire" bombing of Canadian troops in Afghanistan that killed four soldiers routinely took amphetamines that may have impaired their judgment, a lawyer for one of the men said on Thursday.
An Air Force spokeswoman said U.S. pilots have used low doses of dextroamphetamine while flying long missions since World War II, but insisted use of the drug was voluntary and safe.
Illinois Air National Guard pilots Majs. Harry Schmidt and William Umbach face a possible court-martial for dropping a laser-guided bomb near Kandahar on April 17 because they thought they were being fired on from the ground.
An Air Force investigation determined the pilots "demonstrated poor airmanship" and ignored standard procedure by not making sure there were no allied troops in the area.<snip>
And it seems that "go pills" were quite common during the first Gulf War also<
http://www.defensetech.org/archives/000188.html> at least among pilots.
Your casual dismisal of this phenomenon is not based in any sort of reality, in fact quite the opposite. It has been and continues to be a common practice amongst our armed forces to take various forms of amphetamines. Not only a common practice, but one sanctioned by the upper brass.
And let's not even get into the usage of other drugs friend, the evidence for that is overwhelming, even to the most sceptical.