Karl Timmermann was born on June 19, 1922, in Frankfurt am Main, Germany. He grew up in Nebraska, and enlisted in the U.S. Army on July 6, 1940. After completing basic training he was assigned to the 15th Infantry Regiment of the 3rd Infantry Division at Fort Lewis, Washington. As his unit was getting ready to sail for Morocco for Operation Torch, Timmermann was selected to attend Officer Candidate School in October 1942. He graduated and was commissioned a 2d Lt in the U.S. Army Infantry at Fort Benning, Georgia, on February 16, 1943, and he then completed armored infantry training at Fort Riley, Kansas. His next assignment was as a platoon leader in Company A of the 27th Armored Infantry Battalion, 9th Armored Division, and he deployed with his unit to France in September 1944. Lt Timmermann participated in the Battle of the Bulge with his unit in December 1944, and he became Commander of A Company in March 1945. He was awarded the Distinguished Service Cross for his heroism in taking the Ludendorff Railroad Bridge, the first bridgehead across the Rhine River for Allied Forces during the Battle of Remagen on March 7, 1945. After serving on Occupation duty in Germany, he returned to the United States and received an honorable discharge on December 12, 1945. He returned to active duty in the Army as a Technical Sergeant on October 28, 1947, and he served as a recruiter and then as an instructor with he Officers' Reserve Corps in Omaha, Nebraska, and he was recommissioned a 1st Lieutenant on December 26, 1948. He then served with the 7th Mechanized Cavalry Reconnaissance Troop of the 7th Infantry Division at Fort Omaha, and he deployed with his unit during the Inchon Landing during the Korean War in September 1950. After several months of combat, Lt Timmermann was evacuated back to the United States after being diagnosed with cancer. His treatment was unsuccessful, and he died on October 21, 1951, and was buried at Fort Logan National Cemetery in Denver, Colorado.

His Distinguished Service Cross Citation reads:

The President of the United States of America, authorized by Act of Congress July 9, 1918, takes pleasure in presenting the Distinguished Service Cross to Second Lieutenant (Armor) Karl H. Timmermann, United States Army, for extraordinary heroism in connection with military operations against an armed enemy while serving with the 27th Armored Infantry Battalion, 9th Armored Division, in action against enemy forces on 7 March 1945, in Germany. Upon reaching the Ludendorff railroad bridge across the Rhine River, Second Lieutenant Timmermann, aware that the bridge was prepared for demolition, and in the face of heavy machine gun, small arms and direct 20-mm. gun fire, began a hazardous trip across the span. Although artillery shells and two explosions rocket the bridge, he continued his advance. Upon reaching the bridge towers on the far side, he cleared them of snipers and demolition crews. Still braving the intense machine gun and shell fire, he reached the eastern side of the river where he eliminated hostile snipers and gun crews from along the bank and on the face of the bluff overlooking the river. By his outstanding heroism and unflinching valor, Second Lieutenant Timmermann contributed materially to the establishment of the first bridgehead across the Rhine River.