During World War I, the German military was very slow to adapt to the integration of tanks into the war on the Western Front. In fact, they were the last nation on the Western Front to begin a tank program, being beaten by Britain and France and this was one year after said tank programs began.
When they did develop their tank program, the end result was the Sturmpanzerwagen A7V, production of which began in October 1917. It first went into battle in March 1918, providing support for German troops north of the Saint Quentin canal. Three of the tanks broke down and it inability to cross trenches cause it to lag behind the advancing troops. Other flaws in the design of the A7V included it's short tracks limiting it's off road performance and it's high centre of gravity causing it to tip over or get stuck.
Only 20 A7V tanks were built and due to their problems, were only valuable as a propaganda tool, rather than as a proper weapon of war.
Eventually, the Germans decided to commandeer Allied tanks, repaint them with German colours and use them in the battlefield. These stolen tanks were called Beutepanzers.
However, the use of Beutepanzers itself had problems. they were unable to be resupplied or repaired effectively in the field. The German High Command disliked the use of captured tanks since their cumbersome size and slow speed did not fit with German tactics which favoured speed and aggression.
So, what if the Germans were able to beat the French and British to the punch and be the first to introduce tanks to the battlefield in World War I in 1915 or 1916?