A military band plays at a military base in Bydgoszcz, Poland, on March 9, 2019. The local military base organized events on the occasion of the 20th anniversary of Poland's joining NATO. Poland officially joined NATO in 1999. (Xinhua/Jaap Arriens)

Military personnel teach visitors how to perform CPR in Bydgoszcz, Poland, on March 9, 2019. The local military base organized events on the occasion of the 20th anniversary of Poland's joining NATO. Poland officially joined NATO in 1999. (Xinhua/Jaap Arriens)

A child sits in a gun turret during a military picnic at a military base in Bydgoszcz, Poland, on March 9, 2019. The local military base organized events on the occasion of the 20th anniversary of Poland's joining NATO. Poland officially joined NATO in 1999. (Xinhua/Jaap Arriens)

Senior officers of the Polish defence forces visit an exhibition at a military base in Bydgoszcz, Poland, on March 9, 2019. The local military base organized events on the occasion of the 20th anniversary of Poland's joining NATO. Poland officially joined NATO in 1999. (Xinhua/Jaap Arriens)