Historian Stanley P. Hirshon suggested that Dodge, "by virtue of the range of his abilities and activities," could be considered "more important in the national life after the Civil War than his more famous colleagues and friends, Grant, Sherman, and Sheridan.

While working at a neighboring farm, the 14-year-old Grenville met the owner's son, Frederick W. Lander, and helped him survey a railroad.

[4] Lander was impressed with Dodge and encouraged him to go to his alma mater, Norwich University (in Vermont) where he was a member of Theta Chi fraternity.

[13] Following the Vicksburg campaign, his own troops joined General Grant and Iowa Governor Samuel J. Kirkwood in petitioning for Dodge's promotion.

[18] In December, his forces engaged in a skirmish near Rawhide, twelve miles north of Florence, Alabama that resulted in the capture of 20 prisoners.

Also during the war, he provided information to Thomas Clark Durant who consequently made a fortune[20] smuggling contraband cotton from the Confederate States to fund his intelligence efforts.

After the war, Dodge joined the Military Order of the Loyal Legion of the United States and was assigned insignia number 484.

His first experience with intelligence gathering came when general John C. Fremont sent Dodge's cavalry regiments on useless raids near Rolla, Missouri based solely on rumors.

[4] The initial group, known as the "Corps of Scouts" was formed from men of the 24th and 25th Missouri Infantry Regiments, who were often assigned to their own neighborhoods and were paid for their expenses, although most refused payment due to their Union loyalties.

[23] It was one of the largest of the war, funded by the proceeds of captured Confederate cotton, with over 100 agents, and so effective that their identities remain a mystery even in modern times.

[25] His organization, which later became part of the Union Bureau of Military Information, helped Dodge in short order defeat General John Bordenave Villepigue near the Hatchie River, capture Colonel W.W. Faulkner's command of partisan rangers near Island Number Ten and defeat General Earl Van Dorn at the Battle of Tuscumbia during his service with the Army of the Mississippi, and was later vital in the capture of Vicksburg under Grant.

[28] Dodge would utilize human intelligence from female spies, runaway slaves and unionists living in Confederate territory.

[30] At its peak, his network ran from Georgia (Atlanta and Dalton), to Alabama (Florence, Selma, Decatur, Mobile), to Tennessee (Chattanooga and Columbia) to Mississippi, where information would be reported to Dodge, to Maj. Gen. Richard Oglesby, to Hurlbut in Memphis, to Grant himself, a process of about ten days.

[31] Dodge would later report directly to Grant during the Vicksburg campaign, where he even had agents open Confederate General Joseph Johnston's mail.

Connor's men inflicted a decisive defeat on the Arapaho Indians at the Battle of the Tongue River, but the expedition in general was inconclusive and eventually escalated into Red Cloud's War.

During the 1865 campaign in the Laramie Mountains in Wyoming (known then as the Black Hills), while escaping from a war-party, Dodge realized he had found a pass for the Union Pacific Railroad, west of the Platte River.

In May 1866, he resigned from the military and, with the endorsement of Generals Grant and Sherman, became the Union Pacific's chief engineer and thus a leading figure in the construction of the Transcontinental Railroad.

Dodge had been hired by Herbert M. "Hub" Hoxie, a former Lincoln appointee and winner of the contract to build the first 250 miles of the Union Pacific Railroad.

He made a substantial profit, but when the scandal of Durant's dealings emerged, Dodge removed himself to Texas to avoid testifying in the inquiry.

[4] In 1866, Dodge defeated incumbent Republican John A. Kasson in the nominating convention to represent Iowa's 5th congressional district in Congress.

His time in Washington (during the Fortieth United States Congress), was often spent lobbying on behalf of the Union Pacific, although he supported internal improvements to the West.