An Estonian soldier participates in the annual Spring Storm military exercise in Maidla, northeastern Estonia, on May 18, 2017. Some 9,000 military personnel of the Estonian defense forces as well as allied forces join the exercise from May 8 to May 25. (Xinhua/Sergei Stepanov)

French soldiers participate in the annual Spring Storm military exercise in Maidla, northeastern Estonia, on May 18, 2017. Some 9,000 military personnel of the Estonian defense forces as well as allied forces join the exercise from May 8 to May 25. (Xinhua/Sergei Stepanov)

A German Army armored vehicle participates in the annual Spring Storm military exercise in Maidla, northeastern Estonia, on May 18, 2017. Some 9,000 military personnel of the Estonian defense forces as well as allied forces join the exercise from May 8 to May 25. (Xinhua/Sergei Stepanov)

Estonian soldiers participate in the annual Spring Storm military exercise in Maidla, northeastern Estonia, on May 18, 2017. Some 9,000 military personnel of the Estonian defense forces as well as allied forces join the exercise from May 8 to May 25. (Xinhua/Sergei Stepanov)