McClellan was born on 3 December 1826 in Philadelphia, the son of a prominent surgeon and founder of a medical college. Although schooled locally, he received private tuition in Greek and Latin, and was admitted to the University of Pennsylvania to study law in 1840. Two years later, though, he decided to switch to a military career, and with the help of his father was able to attend the US Military Academy at West Point. He remained there until graduating in 1846. He was commissioned a brevet second lieutenant in the U.S. Army Corps of Engineers, and ordered to sail for Mexico, where he took an active part in the Mexican-American War, being given brevet promotions to first lieutenant and captain.
McClellan returned to West Point as an instructor, training cadets in engineering activities. Among other activities, he served with a 1952 expedition to find the source of the Red River, translated a French manual on bayonet tactics, and was involved in surveying possible routes for a transcontinental railroad. In 1855, he was promoted to captain and assigned to the 1st U.S. Cavalry regiment. He served as an official observer of the European armies in the Crimean War, and subsequently wrote a manual on cavalry techniques. He also developed a new type of saddle. In 1857, however, he resigned from the military to take a position as a chief engineer with the newly constructed Illinois Central Railroad. By 1860, he had become president of the Ohio and Mississippi River Railroad, headquartered in Cincinnati. That same year, after a long courtship, he married Mary Ellen Marcy, and they would have two children.
At the outbreak of the Civil War in 1861, McClellan, despite being a Democrat, offered his services to Abraham Lincoln. He was given command of the volunteer army of the state of Ohio, but was soon promoted to the rank of major general in the regular army. A series of small battles won him the nickname of ‘The Young Napoleon’. He was put in charge of a large number of volunteer forces that he organised into the famous Army of the Potomac. By the end of 1861, he had succeeded Winfield Scott as general-in-chief of the Union Army. Despite his brilliant organising abilities and considerable military successes, he continually showed a reluctance to be more aggressive against the enemy, and failed to follow the demands of the strategy put in place by Lincoln and Edwin M. Stanton (Secretary of War), and was removed from high command of the army. He continued, though, to lead the Army of the Potomac, for a while, but was eventually ordered down from that command as well.
In 1864, McClellan was nominated by the Democratic Party to stand for election as president against Lincoln, but he couldn’t agree with the Party’s position that the war was a failure and should be brought to an end. He won only three states; and he resigned from the army on election day. Subsequently, he sailed for Europe with his family, where they remained until 1868. On his return to the US, he was appointed chief engineer of the New York City Department of Docks in 1870; two years later he became president of the Atlantic and Great Western Railroad. After another three year sojourn in Europe, he returned to be elected as Democratic governor of New Jersey (1978-1981). He spent the last years of his life travelling and writing, and died in 1885. Wikipedia has a long and detailed biography, but there are plenty of others sources of information about McClellan: The Civil War Trust, Home of the American Civil War, History Net, and History.Com.
McClellan wrote and published several books during his lifetime, including autobiographical works. However, a diary he kept as a young man during his Mexican posting was not published until 1917. William Starr Myers, a Princeton University professor and historian, was working on a biography of McClellan when he came across the diary among McClellan’s papers in the Library of Congress. He edited the short journal for publication by Princeton University Press as The Mexican War Diary of George B. McClellan. In his preface, Starr states: ‘It has seemed to me that this diary should prove to be of special value at the present time, for it throws additional light upon the failure of our time honoured “volunteer system” and forecasts its utter futility as an adequate defense in a time of national crisis or danger.’ The book, less than a 100 pages long, is freely available to read at Internet Archive.
Starr provides a brief introduction to the diary, which includes the following: ‘To the student of McClellan’s life this diary presents certain striking contrasts in character between the youthful soldier, not yet twenty years of age, and the general or politician of fifteen or twenty years later. At this time McClellan was by nature happy-go-lucky, joyous, carefree, and almost irresponsible. In after years he became extremely serious, deeply and sincerely religious, sometimes oppressed by a sense of duty. And yet at this early age we can plainly discern many of the traits that stand out so prominently in his mature life. He was in a way one of the worst subordinates and best superiors that ever lived. As a subordinate he was restless, critical, often ill at ease. He seemed to have the proverbial “chip” always on his shoulder and knew that his commanding officers would go out of their way to knock it off; or else he imagined it, which amounted to the same thing. As a commanding officer he always was thoughtful, considerate and deeply sympathetic with his men, and they knew this and loved him for it.
These same traits perhaps will explain much of the friction during the early years of the Civil War between McClellan and Lincoln and also the devotion that reached almost to adoration which the soldiers of the Army of the Potomac showed for their beloved commander. And McClellan had many intimate friends, friends of high character, who stood by him through thick and thin until the very day of his death. This relationship could not have continued strong to the last had he not in some measure deserved it. His integrity, his inherent truthfulness and sense of honor, stood out predominant.’
And here are several extracts from the diary itself.
26 December 1846
‘Marched 20 miles to San Fernando where we arrived a little after sunset. Road level until we arrived within about 5 miles of San Fernando, when it became rocky and hilly but always practicable. About 4 miles from San Fernando we reached the summit of a hill from which we beheld a basin of hills extending for miles and miles - not unlike the hills between the Hudson and Connecticut opposite West Point. About two miles from San Fernando are some wells of pretty good water - the men were very thirsty - Gerber offered a volunteer half a dollar for a canteen full of water. My little mare drank until I thought she would kill herself. The Alcalde and his escort met General Patterson at this place. He was all bows, smiles and politeness. Murphy of whom more anon had the honor of taking San Fernando by storm. He was the first to enter it, mounted on his gallant steed. We first saw San Fernando as we arrived at the summit of a high hill, the last rays of the sun shining on its white houses, and the dome of the “Cathedral” gave it a beautiful appearance. It was a jewel in the midst of these uninhabited and desert hills. We encamped in a hollow below the town had a small eggnog and dreamed of a hard piece of work we had to commence on the morrow. Mañana [tomorrow morning] por la mañana.’
27 December 1846
‘We had our horses saddled at reveille and before sunrise were upon the banks of El Rio de San Fernando - a clear, cold and rapid mountain stream, about 40 yards wide and two and a half feet deep - bottom of hard gravel. We crossed the stream and found ourselves the first American soldiers who had been on the further bank. The approaches to the stream from the town required some repairs, nothing very bad - it was horrible on the other side. As we again crossed the stream we halted to enjoy the beautiful view - the first rays of the sun gave an air of beauty and freshness to the scene that neither pen nor pencil can describe.
With a detail of 200 men and our own company we finished our work before dinner. Walked up into the town in the afternoon. On this day General Pillow overtook us. He had a difficulty with a volunteer officer who mutinied, drew a revolver on the General, etc., etc. The General put him in charge of the guard - his regiment remonstrated, mutinied, etc., and the matter was finally settled by the officer making an apology.’
28 December 1846
‘Crossed the stream before sunrise under orders to move on with the Tennessee horse one day in advance of the column in order to repair a very bad ford at the next watering place - Las Chomeras. Very tiresome and fatiguing march of about 22 miles. Road pretty good, requiring a few repairs here and there. Water rather brackish. Very pretty encampment. Stream about 20 yards wide and 18 inches deep. No bread and hardly any meat for supper.’
29 December 1846
‘Finished the necessary repairs about 12 noon. We partook of some kid and claret with Colonel Thomas. While there General Patterson arrived and crossed the stream, encamping on the other side. Waded over the stream to see the Generals - were ordered to move on in advance next morning with two companies of horse and 100 infantry.’
30 December 1846
‘Started soon after daybreak minus the infantry who were not ready. Joined advanced guard, where Selby raised a grand scare about some Indians who were lying in ambush at a ravine called “los tres palos” in order to attack us. When we reached the ravine the guard halted and I rode on to examine it and look for the Indians - I found a bad ravine but no Indians.
On this same day the Major commanding the rear guard (Waterhouse, of the Tennessee Cavalry) was told by a wagonmaster that the advanced guard was in action with the Mexicans. The men, in the rear guard, immediately imagined that they could distinguish the sound of cannon and musketry. The cavalry threw off their saddle bags and set off at a gallop - the infantry jerked off their knapsacks and put out - Major and all deserted their posts on the bare report of a wagonmaster that the advance was engaged. A beautiful commentary this on the “citizen soldiery.” Had we really been attacked by 500 resolute men we must inevitably have been defeated, although our column consisted of 1700 - for the road was narrow - some men would have rushed one way, some another - all would have been confusion and all, from the General down to the dirtiest rascal of the filthy crew, would have been scared out of their wits (if they ever had any).
Our 100 infantry dodged off before we had done much work, and our own men did everything. We reached Encinal about 4 P. M. after a march of about 17 miles, and almost incessant labor at repairs. It was on this day that General Patterson sent back Brigadier General Pillow to tell Second Lieutenant Smith to cut down a tree around which it was impossible to go!!’
23 March 1847
‘Firing continued from our mortars steadily - fire of enemy by no means so warm as when we opened on the day before. Our mortar platforms were much injured by the firing already. The 24 pounder battery had to be re-revetted entirely - terreplein levelled. During this day and night the magazine was excavated, and the frame put up. Two traverses made the positions of platforms and embrasures determined. Two platforms laid and the guns run in the embrasures for them being partly cut. One other gun was run to the rear of the battery.’
24 March 1847
‘On duty with Captain Saunders again - could get no directions so I had the two partly cut embrasures marked with sand bags and dirt, and set a party at work to cover the magazine with earth as soon as it was finished. During this day the traverses were finished, the platforms laid, the magazine entirely finished, and a large number of sand bags filled for the revetments of the embrasures. The “Naval Battery” opened today, their fire was fine music for us, but they did not keep it up very long. The crash of the eight inch shells as they broke their way through the houses and burst in them was very pretty. The “Greasers” had had it all in their own way - but we were gradually opening on them now. Remained out all night to take charge of two embrasures. The Alabama Volunteers, who formed the working party, did not come until it was rather late - we set them at work to cut down and level the top of parapet - thickening it opposite the third and fourth guns. Then laid out the embrasures and put seven men in each. Foster had charge of two, Coppée of two, and I of two. Mine were the only ones finished at daylight - the Volunteers gave out and could hardly be induced to work at all.’