This was basically the only tank the Germans employed in WWI, they had a frontal armor of 30mm and a side armor of 20mm. This protected agains machine gun and small arms fire, but did not protect against heavier calibers (the steal was not hardened steel like used in the British tanks)
Here a battle report (Forty, George (1995). Tank Action from the Great War to the Gulf. Alan Sutton Publishing Ltd. pp. 39–47. ISBN 0750904798.):
The first tank against tank combat in history took place on the 24 April 1918 when three A7Vs (including chassis number 561, known as "Nixe") taking part in an attack with infantry incidentally met three Mark IVs (two Female machine gun-armed tanks and one Male with two 6-pounder guns) near Villers-Bretonneux.
During the battle tanks on both sides were damaged.
According to the lead tank commander, 2nd Lt Frank Mitchell, the Female Mk IVs fell back after being damaged by armour piercing bullets. They were unable to damage the A7Vs with their own machine guns. Mitchell then attacked the lead German tank, commanded by 2nd Lt Wilhelm Biltz, with the 6 pounders of his own tank and knocked it out. He hit it three times, and killed five of the crew when they bailed out. He then went on to rout some infantry with case shot. The two remaining A7Vs in turn withdrew. As Lt. Mitchell's tank withdrew from action, seven Whippet tanks also engaged the infantry. Four of these were knocked out in the battle, and it is unclear if any of them engaged the retreating German tanks. Lt. Mitchell's tank lost a track towards the end of the battle from a mortar shell and was abandoned. The damaged A7V was later recovered by German forces.
All 18 available A7Vs had been put into action that day with limited results; two toppled over into holes, some encountered engine or armament troubles. After a counterattack, three ended up in Allied hands. One was unusable and scrapped, one used for shell testing by the French, and the third taken by the Australians.
And here a video:
Rattler
