Early in the Civil War, Cobham began recruiting in Warren County following the Union disaster at the First Battle of Bull Run.

Cobham fell ill with typhoid fever in July 1862 and did not rejoin the regiment until October of that year.

Gen. Thomas L. Kane, was taken ill, Cobham led the 2nd Brigade of Geary's division in the Gettysburg Campaign.

Starting without a guide, Geary got lost and took Cobham's and Charles Candy's brigade down the Baltimore Pike in the wrong direction.

Cobham was awarded a posthumous brevet promotion to the rank of brigadier general on July 19, 1864, effective as of the date before his death.

In 1896, the local post of the Grand Army of the Republic convinced the surviving family to allow Cobham's reburial in the GAR plot at Oakland Cemetery, where he rests today.

Cobham's wartime letters to his mother and brother are part of the collections of the Warren County, Pennsylvania Historical Society.