Submarines remain extremely lethal to surface ships, even those with advanced anti-submarine warfare (ASW) systems. Modern air independent propulsion submarines that run on diesel fuel are even harder to track down than nuclear powered submarines which almost never have to surface. If naval warfare ever does break out (there have been just three instances of naval warfare between sovereign states since World War II (specifically the Falklands War in 1982, the last of the Indo-Pakistani Wars in 1971, and war between Iran and Iraq from 1980 to 1988) - "there have been just two submarine kills in the last 62 years. Submarines have damaged civilian ships since World War II, but only by accident.", one submarine kill was in 1982, the other in 1971), the U.S. could abruptly find many of its surface warships sunk in short order by hostile submarines. The flip side of the submarine threat, however, is that there are very few submarines in military service with potentially hostile nations outside of the general vicinity of China and North Korea, and even fewer of those submarines are modern, hard to detect submarines. Conventional weapons treaties might be a less expensive solution in most cases than advanced ASW technology.
Department of Defense weapons system cost bloat is an across the board phenomena. The F-35 is now coming in at $85 million a plane (or more, see below), the DDG-1000 Zumwalt destroyer at $6 billion per ship, and so on. While improved munitions have added a great deal of value in terms of range, lethality, and accuracy, it isn't obvious that the airplanes and ships and tanks that carry these munitions are improved in militarily useful ways that justify their much greater cost. The same source states in a different article that:
[A]ir [F]orce generals point out that the first 500 or so F-35s will cost $200 million each (without taking R&D into account), while F-22s only cost $145 million each (without taking R&D into account). The construction cost of the F-35 will eventually go to about $100 million each as more are produced.
The original budget for the F-35 was $30-$35 million per plane, and the F-35 was supposed to be much cheaper than the F-22. The Air Force has released performance data intended to favor extended F-22 production in lieu of F-35 production. Allegedly, Air Force simulations "indicate the an F-22 would destroy 30 Su-27/MiG-29 type aircraft [be]for[e] getting destroyed. But the F-35 would only have a 3:1 ratio, while the F-15 and F-16 would only have a 1:1 ratio[.]" Skepticism of the Air Force assessments abounds, particularly in light of the modest differences in operational capabilities between the F-22 and F-35 announced to date, somewhat more recent technology in the F-35, and the historical experience of U.S. fighter aircraft designs in the real world, which is vastly superior to what the simulations suggest.
Transport planes are also expensive but get more frequent use:
The U.S. Air Force has ordered another fifteen C-17 transports, paying $194 million for each of them. . . . the C-17 is more in demand during the war on terror than are air force combat aircraft. Only the two dozen AC-130 gunships, and a hundred or so A-10 ground attack aircraft and F-16 fighter-bombers are getting steady work these days. But their workload is nothing compared to the C-17s, which are in constant demand to deliver personnel and material to American troops in Iraq, Afghanistan, and many other places[.]
By implication, air to air combat optimized F-15 and F-22 aircraft, and the Navy's F-18s, are getting virtually no use in combat zones.
Large numbers of aircraft were used in Kosovo, in the early days of the first Gulf War, and in the early days of the Iraq War. But, these episodes, the later two involving multinational alliances, lasted just a few weeks or months, in a single theater of operations in the world at once. Kosovo and the Gulf War also pre-date the widespread use of guided bombs that reduce the number of sorties required. Air to air combat has been exceedingly rare, although not entirely non-existent, since Vietnam, and has mostly involved very small numbers of aircraft on both each side in the post-Vietnam era. Large bombers are used so infrequently and require so little training time, that ancient B-52s are still serviceable and have relatively few flight hours.
The U.S. is developing a new guided tank shell. One hopes this version will prove more militarily useful than the last one (or versions developed but little used by other countries) (bold for emphasis, italics for my editorial addition):
The earliest U.S. tank missile was the U.S. MGM-51 Shillelagh. This was a 60 pound, 152mm missile developed fifty years ago [i.e. 1958]. Guidance technology back then was crude, using infrared signals that required the gunner to keep his sights on the target until the subsonic missile hit. Range was 2,000 meters. The Shillelagh system used a short barrel and could fire a howitzer type round as well. The weapon was used on the Sheridan light tank and a few M60 tanks. Some 80,000 Shillelagh missiles were built, and only two were fired in combat (in 1991). The U.S. found high speed, 105mm and 120mm tank rounds were more effective, and dropped Shillelagh type weapons.
Given the availability of guided artillery rounds, armed drones, and anti-tank planes with "smart bombs," as well as mobility issues for the Army's existing main battle tank, the M1-A1, in mountainous terrain and crossing civilian bridges not built for its weight (as well as a shortage of C-5 and C-17 aircraft that can deploy the M1 overseas at a speed greater than allowed by sealift and rail), it isn't obvious that tanks need this long range guided munition technology as well, and there is no doubt that guided tank shells will be expensive.
Increasingly, the notion that tanks are primarily for use against other tanks is appearing outmoded. Most of the tanks destroyed in the Iraq War were destroyed with aircraft, which are faster and already have guided anti-tank weapons. Tanks, in turn, are increasingly being seen as a means of supplying superior force with impunity against unarmored vehicles, infantry groups, and soldiers using civilian buildings as shelter.