Bruno had more luxuries than the men beneath his command. He was the highest rank a man could achieve in the German Army. Travelling from the front lines back to Berlin was not only a matter of personal luxury, but often times necessity.
As Montenegro, and Serbia both capitulated, and the troops which Bruno was in charge of largely began Gendarme operations while also simultaneously preparing for a war in a new theater. Bruno found himself with little to actually do. In fact, his expertise was actually needed back in the fatherland, checking to see if the preparations he had made in years past had finally been concluded.
For the most part, Bruno's involvement in creating military designs, taken, modified, and improved from his past life had been focused on the Army, as that was more or less the single most important part of the Great War, and was also his primary means of production.
