The Lockheed Martin-built F-35B Lightning II Joint Strike Fighter (JSF) will not be able to carry the necessary number of small diameter bomb (SDB) II weapons due to a design flaw in its internal weapons bay.
According to an Inside Defense report, the joint programme office has confirmed that the F-35 jet's internal weapons bay is too small to fit four of the eight SDB II bombs required.
US Air Force F-35 spokesman Joe DellaVedova told Inside: "This is not a new issue to us.
"We've been working with the SDB II programme office and their contractors since 2007. The fit issues have been known and documented and there were larger and more substantial modifications needed to support SDB II that have already been incorporated into production F-35 aircraft.
"These minor or remaining changes were put on hold until the aircraft reached a sufficient level of maturity to ensure that the needed changes would not adversely impact any ongoing SDB (II) developments."
DellaVedova added that a contract is due to be awarded to Lockheed later this year for the design modification work.
Under the $4.1bn SDB II programme, Raytheon expects to deliver around 17,000 weapons, including 5,000 for the US Navy.
Raytheon SDB II business development executive Jeff White was reported by ITAF as saying that: "SDB II will not be altered to suit the F-35B."
The US Air Force is set to buy 1,763 F35A conventional take-off and landing aircraft and USMC 340 STOVL jets, and 80 F35C CV.
The JSF programme receives funding from the US, UK, Australia, Canada, Denmark, Italy, Netherlands, Norway and Turkey.
Image: Weapons bay of a F-35 mock-up. Photo: courtesy of User:Dammit.