(CNN) Almost 2,500 of the world's most advanced warplanes, with a total price tag of $400 billion, and they may not have a "brain" in the bunch?

That's the fear of federal watchdogs who say problems with the F-35 Joint Strike Fighter's complex logistics software system could lead to a grounding of the entire fleet, not to mention future cost increases and schedule delays.

Documenting risks to the F-35's Autonomic Logistics Information System, which Department of Defense officials have described as the "brains" of the fifth-generation fighter, an April 14 Government Accountability Office report says a failure "could take the entire fleet offline," in part, due to the lack of a backup system.

The report also outlines concerns related to the lack of testing done to ensure the software will work properly by the time the Air Force plans to declare its version of the aircraft ready for deployment this August and the Navy reaches that milestone in 2018.

The Marine Corps declared the first squadron of its F-35 variant ready for combat in July 2015, with the intention of upgrading and resolving the software issues before its first planned deployment in 2017.

Photos: F-35 testing Sailors and distinguished visitors watch an F-35B Lightning II aircraft conduct vertical takeoff and landing flight operations aboard the amphibious assault ship USS Wasp in May 2015. Click through the gallery to see more images from the testing. Hide Caption 1 of 7 Photos: F-35 testing Two F-35B Lightning II fighters complete vertical landings aboard the amphibious assault ship USS Wasp during the opening day of the first session of operational testing in May 2015. As the future of Marine Corps aviation, the F-35B is designed to eventually replace all aircraft from three legacy Marine Corps platforms; the AV-8B Harrier, the F/A-18 Hornet, and the EA-6B Prowler. Hide Caption 2 of 7 Photos: F-35 testing An F-35 B Lightning II fighter lands on the flight deck of the amphibious assault ship USS Wasp during short take-off, vertical landing operations in May. A new Pentagon report says the testing did not adequately reflect conditions the aircraft would face in real operations. Hide Caption 3 of 7 Photos: F-35 testing Marines and sailors aboard the amphibious assault ship USS Wasp secure and refuel an F-35B Lightning II fighter after its arrival for the first session of operational testing. Hide Caption 4 of 7 Photos: F-35 testing Vice Adm. William Hilrides, commander of Naval Sea Systems Command, holds up two fingers to indicate to the F-35B Lightning II pilot to power up for takeoff aboard the amphibious assault ship the amphibious assault ship USS Wasp in May. Hide Caption 5 of 7 Photos: F-35 testing An F-35B Lightning II takes off from the flight deck of the amphibious assault ship USS Wasp during test operations in May. Hide Caption 6 of 7 Photos: F-35 testing Sailors and Marines remove a generator for the F-35B Lightning II aircraft from an MV-22 Osprey assault support aircraft aboard the amphibious assault ship USS Wasp during operational testing in May. A new Pentagon report says the testing highlighted maintenance challenges for the F-35. Hide Caption 7 of 7

But the GAO says there is no guarantee that this integral software component of what is already the world's most expensive weapons system will even be ready by 2019, when the program plans to move into full-rate production.

With an estimated price tag of roughly $400 billion for 2,457 planes, the F-35 program has weathered half a dozen years of testing and experienced myriad hardware malfunctions and software glitches along the way.

Estimated to cost approximately $16.7 billion over the aircraft's 56-year lifespan, the logistics software system is considered one of the three major components that make up the F-35, along with the airframe and engine.

Unlike the airframe and engine, however, the software is not built into the plane itself. Instead, it runs on ground computers to support operations, mission planning, maintenance and sustainability.

When it is fully functional, ALIS is intended to be a program that can be plugged into the aircraft and diagnose any parts that are not working properly in order to simplify the maintenance process. Think of it as a high-end version of the diagnostics your mechanic gets when he plugs your car into the shop computer.

While the single seat F-35 Joint Strike Fighter can still technically fly without this software system working at full capacity, both the GAO and military officials agree that it is critical to the program's overall success and long-term sustainability.

And with the program costs expected to exceed $1 trillion over the course of its lifetime, the Pentagon is banking on the streamlined maintenance capabilities provided by the F-35's logistics software system keep this pricey aircraft in the air for decades.

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But according to the GAO, the DoD does not have a plan in place that will ensure the software will be fully functional by the time the program moves into full-rate production -- a deadline that is generally a requirement for the sustainability and support systems of all weapons programs.

While the DoD has taken steps to address many of the software's smaller functionality issues in between launching major upgrades, the GAO says the Pentagon's tendency to respond to problems on a case-by-case basis, rather than with a holistic approach, could lead to further schedule delays and potential cost increases.

"Program officials said that if ALIS is not fully functional, the F-35 could not be operated as frequently as intended, but a DoD commissioned plan found that schedule slippage and functionality problems with ALIS could lead to $20-100 billion in additional costs," the report said.

Another major concern highlighted by the GAO's findings is that under its current design, all the F-35 data produced by the entire U.S. fleet is routed to a single main operating unit that does not have any backup system or redundancy.

If this main server were to fail it could take the entire F-35 fleet offline, according to the GAO report.

However, Lt. Gen. Chris Bogdon, the F-35 program's executive program officer, insisted that the GAO's findings were not a surprise and that the problems that were highlighted are in the process of being addressed.

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"The F-35 is still in development, and this is the time when technical challenges are expected; however, we believe the combined government and industry team will resolve current issues and future discoveries," he said in a statement obtained by CNN.

Specifically, Bogdon outlined the Joint Program Office's commitment to developing a holistic plan to address issues with the logistics software prior to beginning full-rate production of the aircraft, conducting analysis to improve the reliability of cost estimates and developing a standard, program-wide ALIS training through the life cycle of the program.

Lockheed Martin, the lead defense contractor for the Joint Strike Fighter, said that the development of the F-35's logistics software and the program as a whole remain on pace to be ready in time for full-rate production.

"As ALIS development continues, our focus is on the warfighter and delivering the most effective, efficient fleet management system to sustain the F-35 over the next five decades of operations," said Sharon Parsley, a spokeswoman for Lockheed Martin. "The recommendations by the GAO are in line with the actions already underway in preparation for full-rate production and worldwide sustainment."

But despite reassurances from military officials and defense contractors, critics of the F-35 continue to blast the program as a waste.

Photos: In the U.S. Air Force fleet B-52 Stratofortress – The first versions of this long-range heavy bomber flew in 1954. A total of 744 were built, the last of those in 1962. The Air Force maintains 58 B-52s in the active force and 18 in the Reserve. A single B-52 can carry 70,000 pounds of mixed munitions, including bombs, missiles and mines. The eight-engine jets have a range of 8,800 miles. Hide Caption 1 of 24 Photos: In the U.S. Air Force fleet C-130 Hercules transport – A C-130J Super Hercules from the 37th Airlift Squadron flies over Normandy, France, June 3, 2015. First delivered to the Air Force in 1956, the C-130 remains one of the service's most important airlift platforms. More than 140 are still in active units, with more than 180 in the National Guard and a hundred more in the Reserve. The C-130 is powered by four turboprop engines. Hide Caption 2 of 24 Photos: In the U.S. Air Force fleet AC-130 gunships – The AC-130H Spectre and the AC-130U Spooky gunships are designed for close air support, air interdiction and force protection. Armaments on the Spectre include 40mm and 105mm cannons. The Spooky adds a 25mm Gatling gun. Hide Caption 3 of 24 Photos: In the U.S. Air Force fleet F-22 Raptor – The twin-engine F-22 stealth fighter, flown by a single pilot and armed with a 20mm cannon, heat-seeking missiles, radar-guided missiles and radar-guided bombs, can perform both air-to-air and air-to-ground missions. The service has 183 of the Raptors, which went operational in 2005. Hide Caption 4 of 24 Photos: In the U.S. Air Force fleet The single-engine F-35A is the Air Force's eventual replacement for the F-16 and the A-10. The supersonic jets, which will be able to conduct air-to-air and air-to-ground attacks, are just beginning to enter the Air Force fleet. Here, an F-35 Lightning II from the 34th Fighter Squadron at Hill Air Force Base, Utah, flys at Royal Air Force Lakenheath, England, April 15, 2017. Hide Caption 5 of 24 Photos: In the U.S. Air Force fleet B-2 Spirit bomber – The four-engine B-2 heavy bomber has stealth properties that make it hard to detect on radar. Flown by a crew of two, it has an unrefueled range of 6,000 miles and can deliver both conventional and nuclear bombs. Twenty B-2s are in the active inventory. They joined the fleet in 1997. Hide Caption 6 of 24 Photos: In the U.S. Air Force fleet B-1B Lancer bomber – The four-engine jet can fly at 900 mph and carry the largest payload of bombs and missiles in the Air Force inventory. The Air Force has 62 B-1Bs in the fleet. Hide Caption 7 of 24 Photos: In the U.S. Air Force fleet F-15 Eagle – The F-15 Eagle, the Air Force's main air superiority fighter, became operational in 1975. With a crew of one or two, depending on the model, the twin-engine jets are armed with a 20mm cannon along with Sidewinder or AMRAAM missiles. The Air Force lists 249 F-15 Eagles in its inventory. Hide Caption 8 of 24 Photos: In the U.S. Air Force fleet F-15E Strike Eagle – The Strike Eagle is a version of the air superiority fighter adapted to perform ground-strike missions. With a crew of two, the twin-jet can carry and deploy most weapons in the Air Force inventory and operate in any weather. The F-15E was first delivered in 1988. The Air Force lists 219 in its fleet. Hide Caption 9 of 24 Photos: In the U.S. Air Force fleet A-10 Thunderbolt – The A-10 Thunderbolt jets, nicknamed "Warthogs," are specially designed for close air support of ground forces. Key to their armaments is a 30mm Gatling gun. The pilot is protected from ground fire by titanium armor, and the plane's fuel cells are self-sealing in case of puncture. Hide Caption 10 of 24 Photos: In the U.S. Air Force fleet RC-135U – The RC-135U Combat Sent, based at Offutt Air Force Base, Nebraska, provides strategic electronic reconnaissance information to the president, secretary of defense, Department of Defense leaders and theater commanders. Hide Caption 11 of 24 Photos: In the U.S. Air Force fleet An F-15 Eagle takes off from the Andersen Air Force Base, Guam, flight line as two E-3 Sentries are seen in the background. Hide Caption 12 of 24 Photos: In the U.S. Air Force fleet OV-10 Bronco – A 21st Tactical Air Support Squadron OV-10 Bronco aircraft fires white phosphorus rockets to mark a target for an air strike during tactical air control training. Hide Caption 13 of 24 Photos: In the U.S. Air Force fleet A-29 Super Tucano – An A-29 Super Tucano taxis on the flightline during its first arrival, Sept. 26, 2014, at Moody Air Force Base, Georgia. Afghan Air Force pilots trained on the planes that will be used in air-to-ground attack missions in Afghanistan. Hide Caption 14 of 24 Photos: In the U.S. Air Force fleet KC-135 Stratotanker – The four-engine KC-135 joined the Air Force fleet in 1956 as both a tanker and cargo jet. It can carry up to 200,000 pounds of fuel and 83,000 pounds of cargo and passengers in a deck above the refueling system. More than 400 of the KC-135s are flown by active, Air Guard and Reserve units. Hide Caption 15 of 24 Photos: In the U.S. Air Force fleet F-16 Fighting Falcon – The single-engine jet is a mainstay of the Air Force combat fleet. It can perform both air-to-air and air-to-ground missions with its 20mm cannon and ability to carry missiles and bombs on external pods. More than 1,000 F-16s are in the Air Force inventory. Hide Caption 16 of 24 Photos: In the U.S. Air Force fleet C-17 Globemaster transport – The four-engine jet joined the Air Force fleet in 1993 with a primary mission of troop and cargo transport. Each plane can carry up to 102 troops or 170,900 pounds of cargo. The Air Force has 187 C-17s on active duty, 12 in the Air National Guard and 14 in the Reserve. Hide Caption 17 of 24 Photos: In the U.S. Air Force fleet C-5 Galaxy transport – The C-5, with a wingspan of 222 feet, a length of 247 feet and a height of 65 feet, is the largest plane in the Air Force inventory and one of the largest aircraft in the world. The first versions of the four-engine jet joined the force in 1970. The Air Force expects to have 52 versions of the latest model, the C-5M, in the fleet by 2017. Hide Caption 18 of 24 Photos: In the U.S. Air Force fleet CV-22 Osprey – The Osprey is a tiltrotor aircraft that combines vertical takeoff, hover and landing qualities of a helicopter with the normal flight characteristics of a turboprop aircraft, according to the Air Force. It is used to move troops in and out of operations as well as resupply units in the field. The Air Force has 33 Ospreys in inventory. Hide Caption 19 of 24 Photos: In the U.S. Air Force fleet E-3 Sentry AWACS – AWACS stands for airborne warning and control system. This four-engine jet, based on a Boeing 707 platform, monitors and manages battle space with its huge rotating radar dome. The planes have a flight crew of four supporting 13 to 19 specialists and controllers giving direction to units around the battle space. The Air Force has 32 E-3s in inventory. Hide Caption 20 of 24 Photos: In the U.S. Air Force fleet KC-10 Extender – Based on the DC-10 passenger jet, the triple-engine KC-10 is a gas station in the sky with the ability to carry 75 people and 170,000 pounds of cargo. In its six tanks, the KC-10 can carry up to 356,000 pounds of fuel and dispense it while airborne. The Air Force has 59 KC-10s on active duty. Hide Caption 21 of 24 Photos: In the U.S. Air Force fleet T-38 Talon – The twin-engine jet trainer, used by the Air Force to prepare pilots for the F-15E Strike Eagle, F-15C Eagle, F-16 Fighting Falcon, B-1B Lancer, A-10 Thunderbolt and F-22 Raptor, first flew in 1959. Almost 550 are in the active force. Hide Caption 22 of 24 Photos: In the U.S. Air Force fleet U-2 – The single-engine, single-pilot U-2 is used for high-altitude reconnaissance and surveillance. Flying at altitudes around 70,000 feet, pilots must wear pressure suits like those worn by astronauts. The first U-2 was flown in 1955. The planes were used on missions over the Soviet Union during the Cold War, flying too high to be reached by any adversary. The Air Force has 33 U-2s in its active inventory. Hide Caption 23 of 24 Photos: In the U.S. Air Force fleet WC-135 Constant Phoenix – The four-engine WC-135 is used to fly through airspace to detect the residue of nuclear blasts. "The aircraft is equipped with external flow-through devices to collect particulates on filter paper and a compressor system for whole air samples collected in holding spheres," the Air Force says. It has two of these jets in the active force. Hide Caption 24 of 24

"The GAO's report on the F-35's software problems is just the latest failure for this nearly $1.5 trillion program that is far over budget and well behind schedule," said Rep. Jackie Speier, D-California, a member of the House Armed Services Committee.

A consistent detractor of the F-35, Speier said she is finding it hard to be surprised each time a new problem is found due to the program's history of costly setbacks and delays.

"To continue pouring money into building planes that have ejector seat issues, cyber vulnerabilities, flawed aerodynamics, maintenance problems, an inability to fly at full speed while using weapons, and overheating issues is borderline malfeasance," she said.

Despite the controversy that has swirled around the F-35' development, supporters still tout it as the most lethal and versatile aircraft of the modern era -- intended to conduct air-to-air combat, air-to-ground strikes, intelligence, surveillance and reconnaissance missions.

In addition to the U.S. Air Force, the U.S. Navy, the U.S. Marine Corps, the fighter is also intended for use by 10 foreign countries.