end of the year. On August 15, 2011, the United States again deferred the ROCAF request to purchase 66 new F-16C/Ds but offered an upgrade for ROCAF's older F-16A/Bs to F-16V standard, including AN/APG-83 Scalable Agile Beam AESA radars. Unfortunately, during the upgrade work the F-16A/Bs were found to have rusting issues due to age and Taiwan's climate. The upgrade was to be spread over 12 years, though the Ministry of Defense indicated that it would try to reduce the period. In November 2011, the United States-China Economic and Security Review Commission recommended that new fighters be sold to the ROCAF. Taiwan also baulked at the cost of the radar upgrade, not wanting to be the lead customer paying to develop the V-standard upgrade and also because it will be unable to afford both the upgrade and new fighters, should those be offered. In response to a vote in the US House of Representatives to force sale of C/D models, the ROC MND said that the V-standard upgrade package offered superior capabilities over the C/D model aircraft. Some defense officials said that in light of the PRC's increasing capabilities, only F-35s would be sufficient to defend Taiwan. A Pentagon report corroborated that claim, asserting that the PRC would probably seek to destroy ROCAF airfields in the first stages of any attack, making a STOVL fighter such as the F-35B vital for effective defense. In July 2012, Taiwan's Aerospace Industrial Development Corp. and Lockheed Martin announced plans to establish a maintenance and overhaul center to upgrade and maintain the F-16s in place without having to ship them back to the United States. In 2012 a letter of acceptance was agreed on for a US$3.8 billion deal that included the radars, electronic warfare, structural improvements and new weapons. The Air Force received the first upgraded F-16V in 2018. On April 10, 2019, Air Force Chief of Staff Liu Jen-yuan stated that the Air Force is asking for a total of 66 new-build F-16Vs from the U.S. to replace its aging and obsolete F-5 fighters. On August 20, 2019, the sale of F-16Vs was approved by the State Department and submitted to Congress for approval. The 66 F-16s will be supplied with 75 General Electric F110 engines and 75 AN/APG-83. They will also have new mission computers, datalinks, electronic warfare systems, and compatibility with the Joint Helmet Mounted Cueing System II which Taiwan