US President Donald Trump says he has ordered two nuclear submarines to "be positioned in the appropriate regions" in response to "highly provocative" comments by former Russian President Dmitry Medvedev.

In a warning to Russia, President Donald Trump said Friday he’s ordering the repositioning of two U.S. nuclear submarines “based on the highly provocative statements” of the country’s former

“This is a wonderful tradition, and we’re bringing it back,” Trump said of the fitness test that began in 1956. An executive order Trump signed Thursday says America’s declining health and physical fitness threatens the vitality and longevity of the country.

The test was conducted in U.S. public schools for decades until it was retired by the Obama administration. Here’s what to know about it and why Trump wants it back.