The U.S. Marines' version of the F-35 Joint Strike Fighter was declared ready for combat this year, but the Navy and Air Force are still waiting for the finishing touches to be made on their jets.
The fighter jet has been in development for nearly 15 years and is touted as the most advanced weapons system of the modern era, combining stealth capabilities, supersonic speed, extreme agility and state-of-the-art sensor fusion technology.
The price tag for all these benefits, however, is nearly $400 billion, making the program the most expensive weapons system in world history. To maintain and operate the JSF program over the course of its lifetime, the Pentagon will invest nearly $1 trillion, according to the Government Accountability Office.
The Pentagon is scheduled to purchase 2,443 F-35s, but criticism over the affordability of the program has prompted several lawmakers to reaffirm their desire to purchase the full order of aircraft.
The U.S. military is developing the Boeing KC-46 refueling tanker to replace the aging KC-135 fleet now in use.
The KC-46A Pegasus is designed to carry passengers, cargo and injured military personal and can "detect, avoid, defeat and survive threats using multiple layers of protection, which will enable it to operate safely in medium-threat environments," according to Boeing.
The new KC-46A completed a successful first flight in September 2015, but the program has been criticized for schedule delays and cost overruns since the contract was awarded in 2011.
Boeing plans to build 179 KC-46 aircraft for the U.S. Air Force.
Amid criticism over schedule delays and cost overruns, several lawmakers have pledged to keep the program on track to deliver the planned amount of planes.
Above, the Pegasus tanker deploys its centerline boom for the first time, on October 9, 2015. The boom is the fastest way to refuel aircraft, at 1,200 gallons per minute.
The problem-plagued F-22 Raptor took part in its first combat mission in 2014, hitting ISIS targets in Syria.
The price tag for those jets, which were in development for decades, is a staggering $412 million each -- triple its expected cost, according to the Government Accountability Office.
Originally designed and built to replace other fighter and ground attack aircraft in the U.S. military's arsenal, the radar-evading F-22 is an evolutionary dead end. The Air Force acquired only 188 of them from aerospace maker Lockheed and doesn't plan to have any more produced. However, some lawmakers have called for more F-22s to be built.
The Pentagon awarded the long-awaited contract to build the new Long Range Strike Bomber to Northrop Grumman in October 2015, but just how many bombers will be built and what they will look like still remains to be seen.
Some lawmakers, like GOP presidential candidate Jeb Bush, have called for a fleet of "at least 100" long-range bombers, an effort that would cost at least $1 billion.
Officials have been tight-lipped as to the specific capability expectations for the LRS-B, but indications are that it will be stealth, able to carry conventional and nuclear weapons, and could possibly operate both with and without a pilot.
Air Force Secretary Deborah Lee James said the new long-range bomber will have the ability to launch from the United States and strike any target around the globe to counter advancements in air defense systems by rival nations and emerging threats posed by potential adversaries.
Along with the F-35 Joint Strike Fighter and the KC-46 tanker, the LRS-B is one of the Air Force's top modernization priorities.