The early successes of the German forces in WW2 were, in large part, due to drug use by the troops.
In the 1930’s amphetamines and methamphetamines were widely available over the counter in Germany. When the German army invaded Poland in 1939 some troops used a drug called Pervitin to stay alert and awake. Wehrmacht doctors recognised the value of the drugs in the short term and recommended them to high command. They were issued widely, but particularly to the troops most crucial to the Blitzkrieg tactics ; the tank crews and aircrews.
The allies were astounded at the pace and speed of the German advance from the Ardennes to Dunkirk. The famous panzer commander Heinz Guderian said to his troops “I needed you to stay awake for 3 days, you did it for 17.”
OK 17 days is a bit of an exaggeration, but the point is valid. Each night as the French defenders lapsed into sleep, cradling their daily ration of a bottle of red wine, the Germans kept moving forward. Methamphetamines have a number of effects on the human body. As well as keeping you alert and awake they reduce the need for food (pretty handy side benefit for soldiers) and they make you fearless, and more aggressive. It turns regular soldiers into super-troopers.
Mission after mission the Stukas kept bombing, the M-109’s kept strafing and the panzers kept rolling forwards.
The downside of drug use is what happens in the longer term. A short fast campaign, such as that in France in 1940, was perfectly suited to drug use. In longer, drawn out actions the benefits of drug use become counterproductive. As a result the drugs didn’t work on the Russian front.
In wartime military advantages tend to be short term. They are quickly copied by enemies. During the Battle of Britain the British noticed that all the shot-down Luftwaffe aircraft appeared to carry a tube of Pervitin. Analysis determined what it was and the British began to issue similar drugs to their own pilots.
I often wonder how troops today are using highly sophisticated drugs to enhance performance, reduce fear, increase aggression etc. If you face a soldier in a hot situation, just how rational is he/she?