Von Weber's bravery was commended in the diploma accompanying his knighthood: "in the battle of Ypres, in the action at North Poelkapelle on 9 October 1917 when forces were disorganized, [Weber], understanding the urgency of the situation and under most difficult conditions, took command, leading his men in an overwhelming attack on the enemy.
After the war von Weber was drafted into the Reichswehr, where he was first used in an infantry regiment and commanded in 1921 the Prussian Motor Vehicles Department in Berlin.
On 1 March 1930 was posted to the Reich Defence Ministry in Berlin, moving on 1 April 1930 to the local army Weapons Office.
After the start of the Second World War, von Weber fought as a Regimental Commander in the Western campaign against Poland.
On 1 November 1940 Karl Ritter von Weber was promoted to major General, taking over the 17th Rifle Brigade on 1 December 1940, which he commanded until 28 June 1941.