(Bloomberg) -- Lockheed Martin Corp. fell the most in more than four months after the world’s largest weapons maker said software issues will likely delay the start of deliveries of an upgraded version of its F-35 fighter jets.

The defense company said deliveries may slip into the third quarter after previously guiding that the so-called TR-3 version of the F-35 would start shipping in the second quarter. The Pentagon has said it won’t take the upgraded Joint Strike Fighters until issues are fully resolved with the aircraft’s largest and most sophisticated software upgrade.

Lockheed fell 3.9% to $440.87 at 12:29 p.m. in New York, the largest intraday drop since Sept. 6 and one of the leading decliners on the S&P 500.

The company reported fourth-quarter earnings on Monday that beat analyst expectations, while predicting a 6.5% earnings drop for 2024.

The Pentagon is withholding about $7 million in payment to Lockheed for each F-35 that’s been placed in storage while awaiting upgraded software and cockpit hardware. The rebooted technology will allow the fighter jets to carry more precise weapons and gather more information on enemy aircraft and air defenses.

Read more: US Withholds Payment on 21 Lockheed F-35s Over Flawed Software

--With assistance from Tony Capaccio.

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