 The Super Energa could penetrate up to 275 mm (10.8 inches) of armor and 600 mm (23.6 inches) of concrete.Early in the Korean War, U.S. forces found their World War II-era anti-tank rifle grenades were ineffective against the frontal armor of T-34 tanks.This led the U.S. to produce their own version of the Energa, the M28 rifle grenade, from 1950 until 1960.