• [WWI Anti-Tank Weapons and Methods] (http://www.reddit.com/r/AskHistorians/comments/377tza/how_did_soldiers_in_world_war_i_combat_tanks_also/)

• [How did the Germans react to the first use of Tanks?] (http://www.reddit.com/r/AskHistorians/comments/37mhyj/what_was_the_german_reaction_to_the_first_tank/)

These answers I've given should answer your question. In short, while the Tank did cause some panic early on, countermeasures were quickly taken, and it's mechanical unreliability was also noted. It also seems that the Germans had some idea of a 'secret weapon', likely some kind of armoured 'wire crusher', but nothing could prepare them for what they faced, for the firth time, during the Battle of Flers-Courcelettes in September 1916.

Christopher Duffy and Jack Sheldon have both written accounts of the Somme using German sources, and Duffy especially looks at the response to the tank. His book is called Through German Eyes: the British and the Somme; Sheldon's is simply The German Army on the Somme 1914-16.