For 80 years, the initial success of the German military during World War II has been put down to the idea of blitzkrieg, or lightning war.
With a combination of well-coordinated tanks, mechanised infantry and planes, the Germans rapidly rushed into France in 1940, inflicting heavy casualties and ensuring rapid victories.
But Germany had another factor that gave them an edge over the French and British armies that had defeated them on the same turf a generation earlier.
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It was all thanks to something the soldiers and pilots were issued named Pervitin – a pill that would keep them up for days on end.
For the first three days of the invasion, the Germans advanced without pausing to sleep, giving them an extraordinary strategic advantage.
Nowadays Pervitin is better known by a different name – methamphetamine.
German author Norman Ohler, whose book Blitzed: Drugs in Nazi Germany, told 9news.com.au the success of the invasion of France was built around time.
"No sleep, no rest, no pause for the first three days and nights," he said.
"This would have been impossible without methamphetamine."
Not only did Pervitin keep the soldiers and pilots awake, it made them far less hesitant on the battlefield.
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Pervitin was developed by the Temmler pharmaceutical company and was available over the counter in the 1930s in Germany.
It was so popular that it was briefly available in chocolate form.
As part of Germany's preparations to invade France, 35 million tablets were issued to their troops – about ten pills per soldier.
Mr Ohler said the pills were much more pure than the crystal meth available on the street nowadays.
Soldiers were not ordered to take the drugs, but the "Stimulant Decree" issued by High Command showed there was an expectation they would – given they would have to be awake for days on end.
But there was hardly any reluctance from troops.
"Everyone loved Pervitin, so it was not really an issue," Mr Ohler said.
"Like drinking coffee."
In the three days of the initial invasion of France, the Germans had advanced further than they ever did in the four years of World War I.
Soldiers and pilots in the US and UK during World War II were also taking amphetamines, though it was far less widespread.
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Pervitin gave Germany the edge in their blitzkrieg war, but the military soon realised the issues that arose from getting an army hooked on meth.
When high, soldiers became agitated, unpredictable, psychotic and more likely to commit war crimes.
The German military started to scale back access to Pervitin – putting many soldiers into withdrawal.
"People became addicted, and continued to use Pervitin after the war," Mr Ohler said.
One of the Germans hooked on Pervitin was Adolf Hitler himself.
Towards the end of the war, Hitler was being given a cocktail of drugs like morphine, sedatives, body-building supplements, hormones and Pervitin.
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Though he was publicly known as a vehement non-smoker, non-drinker and vegetarian, by the end of his life, Hitler was a drug addict.
As the war progressed, Hitler became famously erratic and paranoid, raging at his generals and issuing bizarre orders.
By the end of 1944, the British had a plan in place to assassinate Hitler.
They decided against it, because Hitler's decision making was so poor that they concluded the Allies would win the war faster with Hitler in charge of Germany.
The last footage of Hitler before the fall of Berlin shows him shaking uncontrollably, suggesting he was in withdrawal in the days before his death.
Pervitin, despite its reputation, remained available to German soldiers for decades to come.
Troops in East Germany could access the drug up until the 1980s.
Criminalisation would not come until the fall of the Berlin Wall.
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