 Complete the following phrase:  Early in 1916, all 42 cm guns were assigned to the 5th Army, which amassed a total of 24 siege guns, the highest concentration of them during the war. The Battle of Verdun was opened on 21 February 1916 with an intense, nine-hour long artillery barrage. The 42 cm guns were tasked with suppressing the artillery of Forts Vaux, Douaumont, Souville, and , but were unable to penetrate the concrete of the modern fortresses. On the second day of the battle, both of KMK Battery 7s M-Gerät guns were destroyed by premature detonations and KMK Batteries 5 and 6 both lost an M-Gerät each to the same cause. Most of the siege guns at Verdun were moved north in July to participate in the 