Key point: By utilizing its massive industrial and technological base, America was able to produce some excellent weapons.
The secret of American victory in World War II was quantity and quality. Copious amounts of weapons and equipment that not only overwhelmed and outmatched the Axis arsenal, but helped enable Lend-Lease allies like Britain and Russia to do the same.
Not that every U.S. weapon was great. The ubiquitous M-4 Sherman tank was plentiful but mediocre. Early U.S. fighters like the P-40 and P-39 were nothing to brag about (except in the hands of the Flying Tigers), while U.S. submarine torpedoes had a bad habit of not exploding until late 1943.
But utilizing its massive industrial and technological base, America was able to produce some excellent weapons, including:
Shell fuzes aren't usually thought of as weapons. But Japanese pilots and German infantrymen learned otherwise.
The issue was that in an era when most anti-aircraft guns lacked radar or sophisticated fire control computers, their chances of hitting a target were not great. So complex were the calculations required to compute where to intersect the path of shell and airplane two to five miles high that tens of thousands of rounds had to be fired on average to score a hit.
The problem became really acute when American warships encountered Japanese kamikazes; destroying an aircraft hell-bent on crashing into your ship meant the suicide planes had to be shot down quickly.
Then someone had the bright idea of putting a tiny radar in the nose of each anti-aircraft shell. Instead of having to strike the aircraft to be effective, the shell could be set to explode once the onboard radar sensed the target was close enough, spraying a cloud of fragments that covered a wider area. The VT (variable time) fuze helped the U.S. Navy survive the kamikaze threat.
It also helped the hard-pressed U.S. Army at the Battle of the Bulge. Artillery shells are more effective if they detonate as airbursts above the ground, rather than bury themselves in the earth. Instead of spraying airplanes, clouds of shrapnel sprayed German infantry.
At the start of World War II, armies used bolt-action rifles that in some cases dated back to the nineteenth century.