After a delay of four days the offer was accepted, and as a colonel of Massachusetts militia he was directed to enlist in the west part of Massachusetts and in the neighbouring colonies the men necessary for the undertaking. He was forestalled, however, by Ethan Allen (q.v.), acting on behalf of some members of the Connecticut Assembly. Under him, reluctantly waiving his own claim to command, Arnold served as a volunteer; and soon afterwards, Massachusetts having yielded to Connecticut, and having angered Arnold by sending a committee to make an inquiry into his conduct, he resigned and returned to Cambridge. He was then ordered to co-operate with General Richard Montgomery in the invasion of Canada, which he had been one of the first to suggest to the Continental Congress. Starting with 1100 men from Cambridge on the 17th of September 1775, he reached Gardiner, Maine, on the 20th, advanced through the Maine woods, and after suffering terrible privations and hardships, his little force, depleted by death and desertion, reached Quebec on the 13th of November.
The garrison had been forewarned, and Arnold was compelled to await the coming of Montgomery from Montreal. The combined attack on the 31st of December 1775 failed; Montgomery was killed, and Arnold was severely wounded. Arnold, who had been commissioned a brigadier-general in January 1776, remained in Canada until the following June, being after April in command at Montreal.Some time after the retreat from Canada, charges of misconduct and dishonesty, growing chiefly out of his seizure from merchants in Montreal of goods for the use of his troops, were brought against him; these charges were tardily investigated by the Board of War, which in a report made on the 23rd of May 1777, and confirmed by Congress, declared that his “character and conduct” had been “cruelly and groundlessly aspersed.” Having constructed a flotilla on Lake Champlain, Arnold engaged a greatly superior British fleet near Valcour Island (October 11, 1776), and after inflicting severe loss on the enemy, made his escape under cover of night. Two days later he was overtaken by the British fleet, which however he, with only one war-vessel, and that crippled, delayed long enough to enable his other vessels to make good their escape, fighting with desperate valour and finally running his own ship aground and escaping to Crown Point.
The engagement of the 11th was the first between British and American fleets. Arnold’s brilliant exploits had drawn attention to him as one of the most promising of the Continental officers, and had won for him the friendship of Washington. Nevertheless, when in February 1777 Congress created five new major-generals, Arnold, although the ranking brigadier, was passed over, partly at least for sectional reasons—Connecticut had already two major-generals—in favour of his juniors. At this time it was only Washington’s urgent persuasion that prevented Arnold from leaving the service. Two months later while he was at New Haven, Governor Tryon’s descent on Danbury took place; and Arnold, who took command of the militia after the death of General Wooster, attacked the British with such vigour at Ridgefield (April 27, 1777) that they escaped to their ships with difficulty.In recognition of this service Arnold was now commissioned major-general (his commission dating from 17th February) but without his former relative rank. After serving in New Jersey with Washington, he joined General Philip Schuyler in the Northern Department, and in August 1777 proceeded up the Mohawk Valley against Colonel St Leger, and raised the siege of Fort Stanwix (or Schuyler). Subsequently, after Gates had superseded Schuyler (August 19), Arnold commanded the American left wing in the first battle of Saratoga (September 19, 1777). His ill-treatment at the hands of General Gates, whose jealousy had been aroused, led to a quarrel which terminated in Arnold being relieved of command. He remained with the army, however, at the urgent request of his brother officers, and although nominally without command served brilliantly in the second battle of Saratoga (October 7, 1777), during which he was seriously wounded. For his services he was thanked by Congress, and received a new commission giving him at last his proper relative rank.In June 1778 Washington placed him in command of Philadelphia. Here he soon came into conflict with the state authorities, jealous of any outside control. In the social life of Philadelphia, largely dominated by families of Loyalist sympathies, Arnold was the most conspicuous figure; he lived extravagantly, entertained lavishly, and in April 1779 took for his second wife, Margaret Shippen (1760-1804), the daughter of Edward Shippen (1729-1806), a moderate Loyalist, who eventually became reconciled to the new order and was in 1799-1805 chief-justice of the state. Early in February 1779 the executive council of Pennsylvania, presided over by Joseph Reed, one of his most persistent enemies, presented to Congress eight charges of misconduct against Arnold, none of which was of any great importance.
Arnold at once demanded an investigation, and in March a committee of Congress made a report exonerating him; but Reed obtained a reconsideration, and in April 1779 Congress, though throwing out four charges, referred the other four to a court-martial. Despite Arnold’s demand for a speedy trial, it was December before the court was convened. It was probably during this period of vexatious delay that Arnold, always sensitive and now incited by a keen sense of injustice, entered into a secret correspondence with Sir Henry Clinton with a view to joining the British service. On the 26th of January 1780 the court, before which Arnold had ably argued his own case, rendered its verdict, practically acquitting him of all intentional wrong, but, apparently in deference to the Pennsylvania authorities, directing Washington to reprimand him for two trivial and very venial offences. Arnold, who had confidently expected absolute acquittal, was inflamed with a burning anger that even Washington’s kindly reprimand, couched almost in words of praise, could not subdue.It was now apparently that he first conceived the plan of betraying some important post to the British. With this in view he sought and obtained from Washington (August 1780) command of West Point, the key to the Hudson River Valley. Arnold’s offers now became more explicit, and, in order to perfect the details of the plot, Clinton’s adjutant-general, Major John André, met him near Stony Point on the night of the 21st of September. On the 23rd, while returning by land, André with incriminating papers was captured, and the officer to whom he was entrusted unsuspectingly sent information of his capture to Arnold, who was thus enabled to escape to the British lines. Arnold, commissioned a brigadier-general in the British army, received £6315 in compensation for his property losses, and was employed in leading an expedition into Virginia which burned Richmond, and in an attack upon New London (q.v.) in September 1781.
In December 1781 he removed to London and was consulted on American affairs by the king and ministry, but could obtain no further employment in the active service. Disappointed at the failure of his plans and embittered by the neglect and scorn which he met in England, he spent the years 1787-1791 at St John, New Brunswick, once more engaging in the West India trade, but in 1791 he returned to London, and after war had broken out between Great Britain and France, was active in fitting out privateers. Gradually sinking into melancholia, worn down by depression, and suffering from a nervous disease, he died at London on the 14th of June 1801.Arnold had three sons—Benedict, Richard and Henry—by his first wife, and four sons—Edward Shippen, James Robertson, George and William Fitch—by his second wife; five of them, and one grandson, served in the British army. Benedict (1768-1795) was an officer of the artillery and was mortally wounded in the West Indies. Edward Shippen (1780-1813) became lieutenant of the Sixth Bengal Cavalry and later paymaster at Muttra, India. James Robertson (1781-1854) entered the corps of Royal Engineers in 1798, served in the Napoleonic wars, in Egypt and in the West Indies, and rose to the rank of lieutenant-general, was an aide-de-camp to William IV., and was created a knight of the Hanoverian Guelphic order and a knight of the Crescent. George (1787-1828) was a lieutenant-colonel in the Second Bengal Cavalry at the time of his death. William Fitch (1794-1828) became a captain in the Nineteenth Royal Lancers; his son, William Trail (1826-1855) served in the Crimean War as captain of the Fourth Regiment of Foot and was killed during the siege of Sevastopol.
Encyclopedia Britannica, 1911