Dr. Jonathan Letterman was born in Canonsburg, Washington County, Pennsylvania, on December 11, 1824. His father being a surgeon, Jonathan and his younger brother William were exposed to medicine at an early age. Letterman's studies were conducted by a private tutor until he entered Jefferson College in 1842. He subsequently graduated in 1845. Eager to follow in his father's footsteps, Letterman pursued his medical studies and graduated from Jefferson Medical College, Philadelphia, in March 1849. In that same year, he passed the examination by the Army Medical Board and was appointed assistant surgeon on June 29. As an assistant surgeon and a captain, Letterman served in Florida in campaigns against the Seminole Indians until March 1853 after which he was transferred to Fort Ripley, Minnesota. In May 1854, he marched with troops from Fort Leavenworth, Kansas, to New Mexico where he served at Fort Defiance against the Navajo Indians and participated in Colonel Loring's campaign against the Gila Apaches. In the autumn of 1859, Letterman was finally granted a leave of absence after a four year term of service on the frontier. This reprieve was short-lived as Letterman was deployed to Fort Monroe, Virginia, in 1859. In 1860, Letterman found himself involved in another campaign; however, this time it was Major Carleton's expedition against the Pah Ute tribe.

In November 1861, Letterman left California for New York City and was placed on duty with the Army of the Potomac with which he stayed until May 1862 after being made Medical Director of the Department of West Virginia. On June 19 of the same year, Letterman was promoted to full surgeon and major and was assigned to succeed Charles Tripler as medical director of the Army of the Potomac by order of Surgeon General William A. Hammond. Although the Secretary of War Edwin M Stanton originally objected to Hammond's choice for medical director, Letterman was given a very convincing endorsement from both the Surgeon General Hammond and his army commander George B. McClellan. Hammond had this to say in his letter that notified Letterman of his appointment:

Sir:

You are detailed for duty with the Army of the Potomac as Medical Director. In making this assignment, I have been governed by what I conceive to be the best interests of the service. Your energy, determination, and faithful discharge of duty in all the different situations in which you have been placed during your service of thirteen years, determined me to place you in the most arduous, responsible and trying position you have yet occupied.

W.A. Hammond, Surg-Gen'l, U.S.A

At the time of Letterman's appointment the Army of the Potomac had suffered heavy casualties at Harrison's Landing on the James River, where the army had retired after the Peninsula campaign. Dr. Letterman's previous service on the frontier and in Indian expeditions had exposed him to the trials and tribulations of military life. It also gave him insight into the personal needs and requirements of the soldiers and as such, Letterman intended to make the resources the soldiers so desperately needed available on a larger scale than ever before. In his report, General McClellan said "the nature of the military operations had also unavoidably placed the Medical Department in a very unsatisfactory condition. Supplies had been almost exhausted or necessarily abandoned; hospital tents abandoned or destroyed and the medical officers deficient in numbers or broken down by fatigue." It was especially difficult since the Union Army entered the war with only 98 medical officers. This was so because more than half of these medical professionals resigned to join the South after the start of the war. These doctors left because at the time promotion was based only on seniority and not merit; this frustrated the doctors and persuaded them to leave.

Despite these and other disadvantages, Dr. Letterman focused most of his attention on the removal of the sick and wounded from the Peninsula, enforcing sanitary measures for improving and maintaining the health of the soldiers and on providing medical supplies. His orders were concise and practical and even his superior officer General McClellan praised Letterman's efforts in his report: "All the remarkable energy and ability of Surgeon Letterman were required to restore the efficiency of his department; but before we left Harrison's Landing he had succeeded in fitting it out thoroughly with the supplies it required, and the health of the Army was vastly improved by the sanitary measures which were enforced at his suggestion."

The army was in desperate need of an ambulance corps. At the time, the "system" for the management of ambulances was neither thorough nor well organized because there was no authority to oversee their use. The ambulances consisted of crude wagons that were often overloaded with wounded men who were tossed about like ragdolls whenever the wagons jolted over the muddy roads towards the Potomac. These ambulances had civilian drivers who were terrified of the battlefield and left without picking up the wounded. Seeing this, Letterman immediately drew up a plan for the organization of an Ambulance Corps, which was approved by General McClellan and published in General Orders on August 2, 1862.

First, Letterman formed separate ambulance trains and assigned them to division level. Each train consisted of 40 ambulances and was under the command of a Lieutenant. The Ambulance Corps was divided into three divisions according to the divisions of troops of each army corps and use of these ambulances was restricted to the designated purpose of picking up the wounded; although they were sometimes used for transporting medical supplies in urgent cases. Eventually these ambulances were habitually used for the transport of supplies to the brigades and regiments. Letterman assigned men to be permanent drivers and he instituted a standard requirement of training for the drivers. Next, Letterman devised field hospitals on the division level by removing surgeons from the regimental level and assigning them to division level hospitals. Each one was tested and was assigned to duty that reflected their skill level. Next Letterman established field-dressing stations where patients were divided into categories according to the severity of their wounds and were treated. Letterman's system of organizing patients into those who would live regardless of their wounds and those who would die from their wounds is used to this day and is known as triage.

Battlefields that were not yet introduced to the Letterman system were forced to tolerate inefficient and abusive systems of Ambulance use. For example, on August 29, 1862 it was discovered that three thousand wounded were left on the field for three days and six hundred were left for a week. This was because the ambulance drivers who replaced the civilians picked the pockets of the wounded, stole alcohol from the medical supplies and left the injured to die. As if that was not bad enough, the Sanitary Commission could not find a single record of wounded soldiers reaching their destinations after the battle of Bull Run in Virginia. As a result of these and other scandals, Letterman's system was gradually adopted by all Union Armies.

The Army of the Potomac was later transferred from the Peninsula to Alexandria, Virginia, where Dr. Letterman discovered that the supplies were few and deficient. It was then realized that the rapid and rushed transfer of the army caused supplies and ambulances to be lost or left behind. The medical officers and officers of the Ambulance Corps were also very weary. Yet, the Army of the Potomac marched into Maryland and fought the battle of Antietam under these disadvantageous conditions in September 1862. It was here that the value of Letterman's brilliant new Ambulance Corps system was shown. After that battle, Dr. Letterman decided to make the method of getting medical supplies more efficient. He reduced the amounts of medicines and materials to be carried and reduced the number of wagons used to transport them by half of the previous numbers; thus making the transport system more compact. The details of this new arrangement were published on October 4, 1862 and were republished on September 3, 1862 and these new arrangements were held in such high esteem that no changes were ever found to be necessary. Additionally, Letterman increased the accountability of the medical department by two principle means: medical inspections and detailed reports by the inspectors.

On October 30, 1862 Letterman established field hospitals while the Army of the Potomac was still in Maryland and this system was carefully designed to work with the Ambulance Corps and the method of supply as a whole. It was at the Battle of Fredericksburg that this holistic approach saw its first opportunity to prove its worth. Those who were a part of the conflict testified to the system's effectiveness. Surgeon Charles O'Leary, then Medical Director of the Sixth Corps said in his report: "Being appointed Medical Director of the Sixth Corps a few days prior to the Battle of Fredericksburg, December 13, 1862, I had the opportunity of putting in operation the Field-Hospital organization devised by the Medical Director of the Army of the Potomac, and witnessing its beneficial results. Within a very few hours after the positions were designated for the Field Hospitals on December 12, all the necessary appliances were on hand, and the arrangements necessary for the proper care of the wounded were as thorough and complete as I have ever seen in a civil hospital."

During the Battle of Gettysburg in July, Letterman had established a General Hospital and temporary field hospitals wherever there was a source of water and shelter. The buildings used ranged from churches, farm buildings and private homes. Sometimes the only shelter available was trees or a piece of canvas strung between poles. As the battle approached its end, there were approximately 22,000 wounded from both the Union and Confederate armies to deal with. Medical supplies were running low and the hardships of the wounded were equally matched with the exhaustion of the doctors. The site chosen for "Camp Letterman" hospital was on the Wolf Farm a little over a mile from Gettysburg on the York Pike. Although his previous service had exposed him to the turmoil of the battlefield, Letterman could not help but feel devastated by what he called "a vast sea of misery." Although Camp Letterman was primitive by modern standards, it was impressive to the soldiers. Each tent held forty folding cots with mattresses and sheets which was a luxury for soldiers who were used to lying on hard ground since being wounded.

In October 1863, Dr. Letterman was given a short leave from duty and married Mary Lee from Maryland who was closely connected to some of the wealthiest and most influential families in Maryland and Virginia at that time. Dr. Letterman was pleasantly surprised when he was presented with an elegant service of silver from the Medical Officers of the Army of the Potomac, along with a note expressing feelings of kindness and gratitude. Letterman then expressed his pride in being an officer of the Army of the Potomac and his gratitude for the kindness that his subordinates showed him.

After being relieved from duty with the Army of the Potomac, Letterman was assigned as Medical Inspector of Hospitals in the Department of the Susquehanna until he resigned from the army in December 22, 1864. He was twice recommended by General McClellan and the Surgeon General for brevet for his services. He continued to practice medicine in California. After the death of his wife Mary, Jonathan Letterman became depressed and eventually died from a chronic intestinal disease on March 15, 1872 in San Francisco, California. When the news of Letterman's illness became public, his friends and former troops rushed to his bedside, but the display of devoted friendship was not enough to save his life. His body and that of his wife are buried side by side in Arlington National Cemetery.

On November 13, 1911 the Army hospital at the Presidio of San Francisco was named Letterman Army Hospital in his honor. There is also a tablet on York Road near Gettysburg to commemorate Dr. Letterman and Camp Letterman General Hospital. Unfortunately, commercial growth in Adams County and around Gettysburg has destroyed most of the Camp Letterman site and all traces of the of the camp are gone except a small portion for the wood lot adjacent to the memorial tablet, erected by the United States War Department. Dr. Jonathan Letterman has become known as the Father of Battlefield Medicine because of his numerous contributions to the medical field and to the army during his lifetime.