When Union and Confederate soldiers went off to war, they left their homes, belongings, and loved ones behind in order to defend their beliefs and homelands. In some cases though, they were able to bring some friends along. There are many historical instances where animals joined troops as mascots in order to inspire the troops or to stand as reminders of their homeland. 
Dogs were commonly used as mascots during the Civil War. Truly “Man’s Best Friend”, dogs lifted the general mood of the soldiers who were far from home. One famous example is Sallie, the mascot of the 11th PA Volunteer Infantry Regiment, trained in West Chester, Pennsylvania. The men all grew to love her and it was said that “there were only three things she had a distaste for, Rebels, Democrats, and women.”  She followed the men into battles and would stay with the bodies of men who had fallen in battle. Sallie herself was shot and killed during the battle of Hatcher’s Run. She held such a special place in her infantry’s heart, that on the monument memorializing the men who died in from that infantry there is a small bronze statue of a dog – Sallie. This gives an insight into value of companionship in the war, and also shows human nature – even after a war where we fought and killed other humans, kindness and innocence was memorialized in this monument of a beloved animal.
Having dogs had its advantages, but they were not the most useful animal during the Civil War. Horses were an advantage on the battlefield, giving soldiers speed and height. They also had a bond with their owners. Robert E. Lee and his horse, Traveller, were a team on the battlefield. His troops often remarked at how close Lee was to his horse. Traveller’s colors were shades of grey, making him “a true Confederate.” He blended in with the grey in Lee’s uniform and connected them.  This relationship between horse and rider not only gave soldiers’ battlefield companionship, but also an emotional connection with their creatures when riding onto the battlefield.
Apparently, not all animals were welcome during the Civil War. In a more amusing account, President Lincoln wrote a letter to the King of Siam, politely rejecting his offer to send a supply of elephants to help with war efforts. He wrote:
I appreciate most highly Your Majesty’s tender of good offices in forwarding to this Government a stock from which a supply of elephants might be raised on our own soil. This Government would not hesitate to avail itself of so generous an offer if the object were one which could be made practically useful in the present condition of the United States. . . Our political jurisdiction, however, does not reach a latitude so low as to favor the multiplication of the elephant, and steam on land, as well as on water, has been our best and most efficient agent of transportation in internal commerce. 
The letter is amusing and fun to historians now, but also gives an interesting “what if” scenario to think about.
Seeing something as simple as having pets around during war time really puts things into perspective when it comes to the needs and wants of Civil War soldiers. The fact that a dog or a horse could be a major factor in uplifting a large group of men is a reminder that yes, these were soldiers fighting in a war, but they were also humans, missing their homes and their loved ones. The value that the men put on these pets gives insight into human nature and could also reflect toward feelings and emotions that link animals like dogs and horses to broader ideas like patriotism and America.
 “Animal Mascots of the Civil War” Fort Ward Museum and Historic Site. http://alexandriava.gov/historic/fortward/default.aspx?id=40198
 “Sallie, Mascot of the 11th PA Volunteer Infantry Regiment.” http://www.nycivilwar.us/sallie.html
 “Robert E. Lee and his Horse Traveller”
 “Lincoln Rejects the King of Siam’s Offer of Elephants.” Civil War Trust. http://www.civilwar.org/education/history/primarysources/lincoln-rejects-the-king-of.html