Wonder weapons are usually old weapons that finally got to the point where they lived up to their original hype. Take smart bombs. They were invented, and used quite successfully, during World War II. But these were radio controlled, and required skilled operators to succeed. Expensive as well, and no one wanted to spend the money to train effective operators in peacetime. In wartime, price was no object, and experience was easy to get. But the U.S. dropped smart bombs after World War II, and didn't revive them until the 1960s, when lasers (developed a decade earlier) were used to bounce their light off a target, and a bomb, equipped with a seeker that could home on the reflected laser light, to hit the target without an operator. This was cheaper and more effective than the earlier smart bombs. The next big jump, in the 1990s, was the GPS guided bomb, which finally perfected the smart bomb. It took four decades.
Then there was the military helicopter, which came of age in the 1960s. But the first helicopter flight took place over half a century earlier, in 1904. The French designers got their chopper off the ground briefly, and that was about it. It took another three decades before practical helicopters were ready for regular use. The Germans sent 20 of their Fl 282s to the Balkans in 1943, where they were used for courier work, especially carrying things between ships at sea, and land bases. Later, the Germans used their helicopters for artillery spotting, although it was cheaper to use single engine fixed wing aircraft. In 1944, the U.S. sent some of their newly developed R-4 helicopters to the Pacific. One of the first missions an R-4 undertook was rescue of downed aircrew in the mountains of Burma. The U.S. produced 400 of their R-4 model before the war ended, and many reached the combat zone.
It wasn't until a decade later, when the gas turbine (jet engine) powered UH-1 was designed, that the first truly effective military helicopter was available. Production began in the late 1950s, and by the early 1960s, the army was enthusiastically adopting the UH-1 for all sorts of missions no one had ever considered before.
The Vietnam war put UH-1 "Hueys" into combat on a huge scale. American UH-1s spent nearly eight million hours in the air during the Vietnam war. A variation of the UH-1, the AH-1G's, or "Huey Cobra" gunships, flew over a million hours. Transporting troops and supplies was the main job for UH-1s, and other helicopters, but there were about half a million medical evacuation missions, that transported nearly a million patients. Helicopters are now considered an essential component of the armed forces.
The anti-tank guided (via a thin wire) missile showed up in the 1950s, and became a fearsome, and popular, weapon by the 1960s. But the Germans had invented the wire guided missile during World War II, for use by German fighters attacking American heavy bombers. The Germans never got that plan into action, but they did invent, and use, thousands of cruise missiles and hundreds of ballistic missiles during World War II. The cruise missile didn't get perfected until the 1980s, while the U.S. and Russia quickly improved German ballistic technology after World War II.
Electronic warfare is seen as the ultimate modern weapon. But, in fact, it got its start in the early 1940s, as German and Allied warplanes fought huge battles over Europe. Nearly all of the modern electronic warfare techniques were invented, and heavily used, during World War II. Since then, the electronic weapons got smaller, more powerful and cheaper. Electronic warfare equipment is often the most expensive component of modern warplanes.
Body armor actually goes back to World War I, but it was only when sturdier and lighter new materials (Kevlar cloth and bullet proof ceramics) merged in the 1990s to produce the first truly bulletproof protective vests, that the troops gained real protection. These are one reason combat death rates in current wars are a third of what they were during World War II.
Combat robots are nothing new either. The modern torpedo, with homing warheads, appeared in World War II. You fired them, and the torpedo guidance system detected the target ship, followed it, and usually sank it. Aerial versions (air-to-air guided missiles) showed up in the 1950s, and everything since then has been making improvements on half century old designs. The American heat seeking Sidewinder missile entered service in the late 1950s, and nothing has been able to replace improvements in that basic design.
While many of these systems are called "wonder weapons," they aren't. That's because every new weapon quickly produces new tactics and combat techniques that reduce the improved capabilities of the new weapons. This is often ignored by historians. Self-preservation is a great motivator, and in the face of new weapons, the enemy will quickly find ways to diminish the wonder.