As Donald Rumsfeld famously said to excuse the lack of appropriate armor on soldiers Humvees in Iraq:
...you go to war with the army you have, not the army you might want or wish to have at a later time...
During explanations for the United States' multi-hundred billion dollar military budget, you'll hear words like "combat ready" and "preparedness", describing how the United States could be invaded at any time, or (more likely) need to invade someone else at a moment's notice. Unfortunately, during this endless period of preparation for an unknown conflict, tremendous expense and effort is wasted in creating and maintaining systems for which there is and sometimes never will be any need.
First, the tank. Tanks, on the face of things, look like something a military should have. Tanks helped win World War II, and tanks look awesome. Legacy, not necessity, states that the US military must maintain a giant fleet of excellent tanks. However, modern warfare isn't fought on slow-moving fronts like World War I and II. Tanks are terrible in the 360 degree urban warfare of the 21st century. They are nothing more than slow-moving, high-value targets. Without a near-limitless budget, and with a war-by-war evaluation of needs, the Abrams tank never would have been considered or built, much less maintained in service for 30 years.
But, considered, built and maintained it was. Mostly because there were armored divisions, and the Patton tank was getting old, not because we were fighting armies with better tanks. It was considered moot, apparently, that nuclear war would not be fought on any front, and any time we were actually facing the Soviet army we would be engaged in nuclear war. There would never be time for tanks, fighting, or deployment. World War III would be fought in an afternoon, and so considerably destroy both sides ability to wage war that there wouldn't be much further discussion.
Second, take a look at the strategic bomber. The B-52 was devised in the late 1940's, has been in service since the mid-1950's, and has never been truly needed. The B-2 stealth bomber was devised in the 1970's and has been used occasionally, but being nearly 40 year-old technology, it doesn't represent the best means of landing a bomb on a target. Putting men in planes and dropping bombs on targets dates back to World War I, and is so much riskier to air crews than launching cruise missiles that it is almost unbelievable we still maintain manned bombers. But, the B-29 was getting old, so the Air Force started looking for the B-52.
Third, fighter jets. The last time a US Air Force pilot was outclassed by another aircraft was in the Vietnam war. Ever since, the airborne threats the USAF has faced have been surface-to-air missiles, or somewhat pathetically, the exact same aircraft they faced in Vietnam. Placing a man in an airplane to go shoot down another airplane has been out-of-date since the early 1970's when surface-to-air missiles really started getting good. Since then fighter pilots have depended on fighting spectacularly poor enemies with no anti-aircraft capabilities, and even then, typically using the fighter jets as light bombers.
What is going on here? There is no role, and there has been no role for fighter jets since the Nixon administration, but still, the F-35 next-next-next-next generation fighter is still being procured (at tremendous expense). Wouldn't it be better to focus on jam-up anti-aircraft missiles?
Finally, the aircraft carrier. The purpose of the aircraft carrier is to be a forward base for the US military anywhere in the world, and its main capability is to launch aircraft carrying ordinance into enemy territory. Consider, though, the ratio of money spent on the chain of systems used to land a warhead on a truck in Iraq and the size and cost of the warhead itself. It would appear that multiple billions of dollars were spent in landing $20 worth of explosives in the lap of the target. Considering that unmanned drones can fly around the world and land ordinance anywhere already, and that the US military has bases in just about every country in the world, what exactly is the boat for? The jets flying off of the boat? Wouldn't a remote control missile launched from a base in Turkey take out 99 of 100 middlemen in the world's most expensive weapons delivery platform?
There is almost self-evidently a better way to accomplish the tasks currently being performed with 1940's strategy, but worse than that, our weapons systems are enormously vulnerable to out-of-the-box thinking that uses modern technology.
In World War II, the Allies were startled by the effectiveness of the so-called Banzai attack. This was nothing more than a fearless, mass charge of Japanese soldiers, frequently after they'd run out of ammunition. Swords drawn, they would rush the British and American soldiers by the hundreds. And, with expert marksmanship and supreme cool, it was possible to repel most attacks for the most part, but between the large number of attackers and small amount of time the Allied soldiers had to shoot all of them before they made contact, the Japanese frequently scored some kills as well. Since World War II, the Banzai attack has reappeared a few times, but most all soldiers prefer to surrender to suicide, and so US military doctrine has not strongly considered massed suicide attack.
But robots don't care if they die.
In every case, between tanks, fighter jets, bombers and aircraft carriers, the concept of massed attacks by very low-value targets has not been considered, and there is no plausible defense planned against thousands of tiny, cheap unmanned attackers.
A jet costs the US taxpayer around $100 million dollars. I can purchase a quadcopter online for $500. That is a 200,000 to 1 ratio of cost. Let's imagine a mass-produced anti-aircraft drone with more serious performance would cost $5000. Now, the ratio is only 20,000 to 1. Imagine a cloud of 10,000 drones, hovering over Tehran. As US aircraft are spotted, each drone would begin to close in, significantly slower than the target jet, but in their masses, they would intercept the jet. They could arrange themselves in a 1 kilometer grid, with one occupying every 20 foot square. Targeting the jet intakes, each individual could move very slowly, and still land exactly where it needed to be at exactly the right time. Even with a 5000 to 1 kill ratio, which the jet fighter is not sufficiently equipped to do, victory belongs to the drones. Even moreso with bombers.
Similarly, rigid inflatable boats with outboard engines and a 600 pound warhead could be sent out by the tens of thousands against an aircraft carrier, for the cost of tens of millions of dollars, as opposed to billions and billions for the aircraft carrier. While the aircraft carrier might be faster, and the grid of destroyers defending it might take down hundreds of the boats, or even thousands, there is simply not enough ordinance on board, nor enough men to target each boat to take down every one of them.
Since no country has the wealth to fight toe-to-toe with the US and create rival aircraft carriers and stealth bombers, they will be forced to take the inexpensive Banzai route. Large, high-value targets will have no place in the battlefield of tomorrow, as thousands of men aboard will be forced to risk their lives to fight off unmanned, nearly zero-value attackers in nearly limitless supply. Even the smaller targets, the Humvees and individual soldiers, may have to consider pigeon-sized drones carrying single-shot .22s and hand grenades, hovering overhead in swarms.