A tragedy in Mississippi has taken the lives of 16 Marines. A transport plane crashed in rural Mississippi and all 16 Marines on board were killed. The KC-130 crashed in Leflore County, about 85 miles north of Jackson, at about 4 p.m. CT, Monday. The cause of the crash remains unknown.

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The flight originated in eastern North Carolina. Its destination has not been announced. CNN is reporting that the plane had stopped in Memphis, Tennessee.

The KC-130 has been the workhorse of American aviation for more than 50 years. It is used for aerial refueling and for transport services. It is a version of the C-130 Hercules.

The planes are often used as gunships, for transports, and ever for firefighting. They’re known for their incredible strength and ability to take off and land on short runways.

The accident left debris on both sides of the highway and slowed down traffic as rescue efforts continued into the night.

The planes were first introduced in 1956 and have flown in every American conflict since. The Marine variant, designated the KC-130, was introduced in 1962.

“While the details of the incident are being investigated, our focus remains on providing the necessary resources and support to the family and friends of these service members as they go through this extremely difficult time,” the Marines wrote in a press report.

President Donald Trump called the crash “heartbreaking” on Twitter. “Melania and I send our deepest condolences to all!” the President tweeted.