My Great-grandfather

My grandfather was born in Russia right after the war. When he was very little, both of his parents passed away, but he still remembered some stories that his father, my great-grandfather, told him of World War II on the Russian front. My great-grandfather was drafted into the military. My grandfather told me that his father didn’t want to leave home and go fight, but he had no other choice. Everyone that was old enough and did not have any serious medical conditions either volunteered, which few did, or were taken away. He was briefly trained and taken to the battlefield, which was in Ukraine. He first fought in Kiev and then in Kharkov.
My grandfather told me of a very interesting story that happened with my great-grandfather. One time my great-grandfather was defending some anti-air guns. He looks over the horizon and sees 20 tanks coming straight at the guns. He reports this to the higher ups and they have no idea what to do because they don’t have any amour piercing guns. They think for a while and decide to do something very drastic- to use the anti-air guns against the tanks! So they lower the guns and aim them through the barrel (looking through the barrel and aiming directly at the tanks). They load up the first gun and fire it. Since the anti-air missiles fire at greater speeds because they need to reach the planes in the sky, the tank was completely obliterated. The Germans thought that the Russians invented a new powerful gun started retreating.