Details are still emerging about a July 15 plane crash thought to be that of a North Korean military aircraft, as reported by UPI's Elizabeth Shim. But there's another mystery afoot — the plane itself, which is rumored to be an Antonov An-2. Why is North Korea still flying a Soviet aircraft that dates from the 1940s, anyway?

Related Content In a Fit of 1940s Optimism, Greyhound Proposed a Fleet of Helicopter Buses

In fact, the An-2 has been part of North Korea's arsenal for a while — it's been linked to other fatal accidents from mounting air-to-surface weapons on the planes. Designed by Oleg Antonov for the Soviets’ Ministry of Forestry, the An-2 first took to the skies in 1947, writes Stephen Dowling for BBC Future. It was supposed to be used for crop dusting and transport. The biplane design includes room for a ton of cargo in the form of soldiers, cows or crops.

The Soviets made about 19,000 of these planes until 1991, when the regime fell, writes Dowling. In the early 2000s, aerospace companies began making them again.

It turns out that the secret of the plane's enduring appeal might be in the model's unique tricks. Dowling reports that the An-2's wings generate a lot of lift, allowing the biplane to take off and land at short distances and fly really, really slowly—meaning they can land just about anywhere while staying literally under the radar. Control surfaces on the wings allow pilots to hover an An-2 when flying into a headwind. In especially strong winds, it can even fly backwards.

North Korea has about 300 An-2s in their air force, according to South Korea’s Chosun Ilbo newspaper. Fuel efficiency and general safety round out the list of qualities that might make them appealing to the North Korean air force.

An-2s might seem old-fashioned, but their unique design still makes them quite stealthy. In fact, using old planes isn't that unusual for the North Korean air force, which is comprised of many planes that might be considered outdated by modern-day pilots. That hasn't kept North Korea from seeking to make updates where possible, though: in April, its air force announced plans to update the color scheme of its An-2s, switching to a new green-topped design to camouflage the vintage planes.