In early December 1862, Bertram found himself as the senior ranking officer in his brigade, though only a lieutenant colonel.[3] He assumed command of the 1st Brigade in Francis Herron's 3rd Division of the Army of the Frontier. and was in command of the brigade at the battle of Prairie Grove. Though Bertram clung to the title of brigade commander during the battle, he realistically commanded no more than the 430 men of his own 20th Wisconsin regiment as the other regiments in his command were detached for temporary assignment elsewhere.
On December 10, 1862, Bertram was promoted to colonel. Despite his promotion he returned to regimental command during the Siege of Vicksburg. He commanded brigades in the Department of the Gulf after the fall of Vicksburg. In August 1864 his brigade was transferred to the Mobile Bay Land Forces under the command of Gordon Granger. There Bertram participated in the land operations during the Battle of Mobile Bay and the Siege of Fort Morgan.
He briefly commanded the District of Southern Alabama before returning to brigade command. His brigade, now part of the XIII Corps, fought in the Battle of Spanish Fort. After the war, he received a brevet to Brigadier General of U.S. Volunteers, backdated to March 13, 1865. He was mustered out of the volunteer service on July 14, 1865.
After the war he returned to Watertown, Wisconsin, and worked as a hotel proprietor. In the 1869, he was elected to the Wisconsin State Assembly from Dodge County's 4th Assembly district, running as an Independent.[4]
Rather than running for re-election to the Assembly in 1870, Bertram was elected Sheriff of Dodge County, and relocated to Juneau, Wisconsin, for that duty. He died suddenly at Juneau in 1878.[2]
