Although the correspondence with the enemy had been kept up nearly eighteen months, it had always been under fictitious names by both parties. The epistolary intercourse between Major André and Mrs. Arnold, begun before her marriage and continued after that event, afforded a convenient medium of communication, which Arnold could turn to his purpose without exciting the suspicions even of his wife. His advances were made directly to Sir Henry Clinton, through the hands of Major André; and in this channel the correspondence was conducted to the end. André had the entire confidence of his commander, and was for a time his aid-de-camp, till raised to a higher station. He affixed to his letters the signature of John Anderson, and Arnold assumed the name of Gustavus. They also wrote in a disguised hand, and used other devices to prevent detection.
Without giving any certain clew to his name, rank, or character, Arnold expressed in his first letters a dissatisfaction with the French alliance, and touched upon other topics in such a manner as he thought would please the British commander and attract his attention. He likewise sent intelligence, which proved to be correct and important. The same was repeated at different times, till at length General Clinton's curiosity was awakened, and he employed every method in his power to ascertain the identity of the person, who was opening himself thus freely, and furnishing information of the greatest value. It was obvious, from the nature of his communications, that he was a person of consequence, who had a knowledge of the secret springs of American affairs, and was on terms of intimacy with the leaders. To prevent the possibility of detection, however, should his letters fall into other hands than those for which they were intended, the language was extremely guarded in every thing that related to the situation or person of the writer.
At length, after putting together and weighing a variety of circumstances, Sir Henry Clinton was satisfied, that his hidden correspondent was General Arnold. He had no positive proof, but the evidence was so conclusive in his own mind, that the correspondence was continued upon that supposition. This discovery was not made, or rather this conviction was not settled till subsequently to Arnold's trial by a court-martial; and being then under a sort of disgrace, and not likely again to be employed, the British commander did not look upon him to be of so much importance, whatever might have been his military merits, that it was an object worthy of his attention to bring him over merely as an officer of rank. On the contrary, believing him to be more useful as a correspondent where he was, than he would be when joined to the British army, no tempting encouragements were held out to hasten his desertion.
Things remained in this posture for some time, when the person wrote, that he should certainly be soon employed again in the American service, and made a direct offer to surrender himself, and in such a manner as to contribute every possible advantage to his Majesty's arms. In a few days Arnold took the command at West Point, and the affair then assumed a magnitude and an interest, which it had not hitherto possessed.
General Clinton now saw a prospect before him, and an opening for a successful operation, which claimed his immediate and assiduous care. To get possession of West Point and its dependent posts, with their garrisons, military stores, cannon, vessels, boats, and provisions, appeared to him an object of such vast importance, that in attaining it no reasonable hazard or expense ought to be spared. In the first place, it would bring under his control the navigable waters of Hudson's River, and in some degree facilitate his intercourse with the army in Canada, as well as essentially derange the communication of the Americans between the eastern and middle States. But other results, of much greater consequence, might be anticipated by taking into view the condition of affairs at the present stage of the campaign.
A French fleet and army, under the command of the Chevalier de Ternay and Count de Rochambeau, had recently arrived in Rhode Island, and were ready to cooperate with the Americans in an attack upon the British, whenever a favorable opportunity should offer. Washington's army had been augmented, and was gaining strength daily by new enlistments and the temporary service of the militia. Many reasons induced Sir Henry Clinton to believe, that an attempt was intended against New York, as soon as a union could be concerted between the commanders of the two allied forces. The information derived from his spies and the Tories confirmed this belief. It was rumored, that Washington would move upon Kingsbridge and Morrisania, while a detachment would menace or perhaps attack Staten Island, and the French invade Long Island and approach the city in that direction.
To execute such a scheme, it would be necessary for the Americans to collect and deposit in some place large magazines of provisions and military stores. Both from its position and its strength, West Point would undoubtedly be chosen for the depot of these supplies. On this ground alone, therefore, it was an object of the greatest importance with the British commander to pursue any plan, which held out a promise to put him in possession of that post. Such an event would not only defeat the project of a combined attack, but distress both the opposing armies to such a degree, by depriving them of supplies, that it would cause disaffection and desertion in the American ranks, and excite a spirit of discontent if not disgust among the French. When these bearings of the subject are taken into view, it is no wonder that Sir Henry Clinton should be extremely desirous to effect a purpose, which would crown the campaign with triumphant success, and be of such immense advantage to the King's service.
His original idea for executing the plan was, that every thing should be in readiness to act when the two allied armies should begin their movements towards New York, and after the magazines had all been gathered into the depots on Hudson's River. If the posts and garrisons had been surrendered at this moment, it would have deranged and frustrated the operations of the allies. Washington must have instantly retreated from Kingsbridge. The French troops on Long Island would have been left unsupported, and must either have retired precipitately to their ships, or more probably have fallen into the hands of the British.
Although Sir Henry Clinton kept the affair a profound secret to himself and two or three officers, yet all the requisite preparations were made. The troops were so posted that they could be put in motion at the shortest notice, and vessels of suitable dimensions and properly manned were ready. While things were in this train, the important news of the defeat of General Gates in South Carolina reached New York. It was questionable at first what course Washington would pursue in consequence of this intelligence. It was supposed, that he would detach a part of his army to the south, and thus change the aspect of the campaign at the north. He was carefully watched by the spies; and it was ascertained, that he did not send a man to the southward, nor make any apparent alteration in his previous plans. It was inferred, that New York was still his object, and this inference was rendered certain by communications from General Arnold. The events, which immediately followed, will be best described in the words of Sir Henry Clinton, as contained in one of his letters to Lord George Germain.
"At this period," said he, "Sir George Rodney arrived with a fleet at New York, which made it highly probable, that Washington would lay aside all thoughts against this place. It became therefore proper for me no longer to defer the execution of a project, which would lead to such considerable advantages, nor to lose so fair an opportunity as was presented, and under so good a mask as an expedition to the Chesapeake, which every body imagined would of course take place. Under this feint I prepared for a movement up the North River. I laid my plan before Sir George Rodney and General Knyphausen, when Sir George, with that zeal for his Majesty's service, which marks his character, most handsomely promised to give me every naval assistance in his power.