He was born in the village of Velikopol'ye of the Ronginsky district, the Mari ASSR. He graduated from 9 classes; the 2nd artillery training regiment – a cadet (August 1941 -December 1942); the 233rd mortar regiment –a battery sergeant 120 mm (December 1942 –May 1943); the 209th mortar regiment – a battery sergeant 120 mm (March 1943 - April 1945); military food point no. 105 –a storekeeper (April 1945 - April 1947). He was the commander of the reconnaissance unit at the mortar regiment in the North-Western front from the 16th of February, 1943, till the 29th of March, 1943; the Bryansk front from the 29th of May, 1943; the Voronezh front from the 28th of July, 1943; the 4th Ukrainian front from the 10th of April, 1945. Wounds: 1 time wounded, 1 time concussed “During the fighting from the 16th of August, 1944, till the 19th of August, 1944, upon the encirclement and destruction of the enemy group in the area of Saydomir on the western bank of the river, in the offensive zone of the 58th guard rifle division of the 3rd guard army of the 1st Ukrainian front, Comrade Grebnev was at the forward observation post, scouted and reported on the observed targets, following all the time in the infantry battle formations. During the fighting he found: 3 easel and 2 light machine guns, an observation post. As a brave scout, he made his way forward despite the enemy's rifle and machine-gun fire up to a platoon of enemy submachine gunners,” - from the award list of the order of “Red Star” on the 19th of August,1944. “During the breakthrough of the enemy defense on the 15th of May, 1945, in the area of the village of Resnitz (Czechoslovakia), in the offensive zone of the 827th fifle regiment of the 302nd rifle division of the 60th army, the 4th Ukrainian front, comrade Grebnev standing at the observation post, detected 2 easel machine-guns, an observation post of the enemy, clot of enemies amounting up to two troops and a anti-tank gun, that all were destroyed by the division’s fire. During an enemy artillery raid he was seriously wounded at the observation post,” - from the award list of the order “Patriotic War of the second degree” dated the 8th of May, 1945. “During the battle on the 3rd of August, 1943, when breaking through the front edge of the enemy's defense in the Belgorod direction, near the farm Vesely, comrade Grebnev organized the work of communication so that during the battle there was a constant connection of the division with the batteries and infantry. Under artillery and mortar fire of the enemy he restored the broken connection 6 times” - from the order on awarding the medal “For Bravery”.