Watch Secret Weapon (2019) HD Full Movie Free on solarmovie.do. Watch Secret Weapon (2019) online free. It's the Second World War. The Red Army had to retreat in a hurry and left their top secret weapon, ...It's the Second World War. The Red Army had to retreat in a hurry and left their top secret weapon, "Katyusha", behind. A group of 8 soldiers is sent to do everything possible not to let "Katyusha" get into the hands of the Germans.