WASHINGTON — U.S. officials are investigating how a shipment of F-35 fighter-jet components bound for the United States was diverted to Hong Kong this summer, an incident that has prompted repeated briefings for congressional national security committees. The shipment was traveling from Australia across the Pacific when it was rerouted, according to three people familiar with the matter who were granted anonymity to discuss private conversations. The Pentagon has confirmed that some components went missing. It remains unclear why the shipment changed course or who currently has the equipment. The parts were being transported by an intermediary for Lockheed Martin, the F-35’s manufacturer. At least one component was a canopy — the transparent cockpit covering that includes a thin radar-absorbing coating central to the aircraft’s stealth capabilities, according to two people familiar with the shipment. The possibility that such a component could be examined by a foreign adversary has heightened concern in Washington. J.J. Gertler, a former House Armed Services Committee staff member and Congressional Research Service military aviation analyst, said access to a physical part could help China verify or refine information obtained through espionage or other means. “Possessing a real one can give them even more to go on,” Gertler said. State Department and Pentagon officials first briefed congressional staff in June, with additional briefings expected in the coming weeks. The State Department declined to comment, while the Chinese Embassy said it was not familiar with the incident. The F-35 Joint Program Office said it was aware of “a shipment issue of unserviceable F-35 Lightning II components.” The office said it was working with U.S. authorities and industry partners to recover the parts, investigate what happened and strengthen safeguards. Lockheed Martin also declined to discuss the shipment’s status, citing security concerns, but said the company follows U.S. regulations governing aircraft components. “Our teams handle every shipment with the utmost diligence and safeguards,” the company said. Hong Kong’s status as a special administrative region of China has added to the sensitivity of the case. Beijing has tightened its control over the city through national security laws and political changes, making the diversion a potential pathway for sensitive U.S. defense technology to enter China’s sphere of influence. The incident also exposes longstanding weaknesses in the F-35’s sprawling international supply chain. The program relies on repair and storage facilities across multiple countries, commercial shipping companies and a shared pool of spare parts used by the United States and allied nations including the United Kingdom, Australia, Denmark, Norway and Poland. Australia has maintenance depots for F-35 aircraft, but none is currently equipped to repair the aircraft’s canopies. Lockheed Martin manages the program’s overall supply chain, while the Defense Department has increased oversight in recent years. A 2023 Government Accountability Office review found that more than 1 million F-35 spare parts had gone missing over the previous five years. The watchdog said the department could not fully review losses worth tens of millions of dollars because Lockheed Martin, rather than the Pentagon, maintained key records for parts in the shared pool. The F-35 program has also faced persistent questions about cost, readiness and performance. Spare-parts shortages have contributed to aircraft being grounded, while sustainment costs have risen. The Pentagon expects the program’s lifetime cost to approach $2 trillion.