The US Marine Corp's first F-35B jump-jet squadron, Fighter Attack Squadron 121, have officially kicked off their training on the new fighter, which will replace the aging (but still awesome) AV-8B Harrier.

"We shifted into IOC [initial operational capability] training last week," squadron CO Lt. Col. Steve Gillette told IHS Jane's on Friday.

According to Jane's, the start of IOC is a big deal for any piece of military hardware, because it's considered the point where a weapon can be safely deployed to troops. With the F-35's checkered history, the start of IOC has been delayed on numerous occasions for all three of the US military's variants.

The Marines are the first of the F-35's three service branches to begin IOC, with the Air Force delaying until the second half of 2016 and the US Navy holding off until August 2018 to February 2019, Jane's said.

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