It seems that Mosby publically defended Stuart for many years, changing over time his conclusions and facts but keeping the essential point clear. At one point in the mid 1880s he was in a public writing battle in The Century Illustrated Monthly Magazine with General Robertson who commanded one of the cavalry brigades sent by Stuart to aid General Lee during his march into the Union. Mosby, in some of his first histories of the events, claimed that Robertson did not perform his duty by giving General Lee proper coverage as ordered. Robertson replied to his remarks and refruted his allegations. Sometime after this Mosby changed his history to include the fact that Robertson had carried out his duties to the satisfaction of General Lee and General Stuart; this change is reflected in the book I am currently reading.
I did a quick search of books published prior to 1900 to see if any other historians believed what Mosby believed and found many...
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The History of the Army of the Potomac, Including That of the Army of Virginia (Pope's), and also the History of the Operations of the Federal Cavalry in West Virginia, 1900, by Charles D. Rhodes 1st Lt. Sixth Cavarly.
[General Lee's letter to Stuart, dated June 22d, gives him these general instructions: "If you find that he [the enemy] is moving northward, and that two brigades can guard the Blue Ridge and take care of your rear, you can move with the other three into Maryland, and take position on General Ewell's right."
And again, in a letter written to Stuart the following day, Lee says: "You will, however, be able to judge whether you can pass around their army without hindrance, doing them all the damage you can, and cross the river east of the mountains. In either case, after crossing the river, you must move on and feel the right of Ewell's troops."
It seems, from these letters and confirmatory statements in letters to General Longstreet, that Lee authorized, if he did not actually suggest, Stuart's raid about the Federal army. But, while giving Stuart great discretionary power, he qualified this power by several important conditions. That Stuart met with hindrances which prevented his keeping in touch with EwelPs right, and even caused his absence from part of the battle of Gettysburg, is a matter of history.]
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The Life and Campaigns of Major-General J.E.B. Stuart: Commander of the Cavalry of the Army of Northern Virginia by Major H. B. McClellan, Cavalry Corps, ANV. 1885
[Colonel John S. Mosby has related in the Philadelphia " Weekly Times " of the 15th of December, 1877, how he submitted to General Stuart, on the 23d, a plan of crossing the Bull Run Mountain at Glasscock's Gap, and of passing through the centre of Hooker's army in Loudon and Fairfax counties, with the purpose of crossing the Potomac at Seneca. While General Stuart does not mention Mosby's name in this connection, there is evidence in his report that this, with some modifications, was the plan which he submitted for the approval of General Lee; for General Stuart states that, before moving from Rector's Cross Roads, he sent Mosby to reconnoitre within the enemy's lines, with orders to report to him on the 25th, near Gum Spring, Loudon County. It is also apparent from Stuart's report that he was not restricted to this one route, but was free to act as circumstances might direct; for he says : —
I submitted to the commanding general the plan of leaving a brigade or so in my present front, and passing through Hopewell, or some other gap in Bull Run Mountain, attaining the enemy's rear, and passing between his main body and Washington, to cross into Maryland and join our army north of the Potomac
General Lee states in his report: —
"Upon the suggestion of the former officer (General Stuart) that he could damage the enemy and delay his passage of the river by getting in his rear, he was authorized to do so."
And again: —
"In the exercise of the discretion given him when Longstreet and Hill marched into Maryland, General Stuart determined to pass around the rear of the Federal army with three brigades, and cross the Potomac between it and Washington, believing that he would be able by that route to place himself on our right flank in time to keep us properly advised of the enemy's movements."
"It was late in the night when a courier arrived from army headquarters, bearing a despatch marked " confidential." Under ordinary circumstances I would not have ventured to break the seal; but the rain poured down so steadily that I was unwilling to disturb the general unnecessarily, and yet it might be important that he should immediately be acquainted with the contents of the despatch. With some hesitation I opened and read it. It was a lengthy communication from General Lee, containing the directions upon which Stuart was to act. I at once carried it to the general and read it to him as he lay under the dripping tree. With a mild reproof for having opened such a document, the order was committed to my charge for the night, and Stuart was soon asleep. It is much to be regretted that a copy of this letter cannot now be produced. A diligent search has failed to find it, and as General Stuart did not forward a copy of it with his report, I presume it was destroyed during our subsequent march. But I have many times had occasion to recall its contents, and I find that my recollection of it is confirmed by several passages in General Stuart's report.
The letter discussed at considerable length the plan of passing around the enemy's rear. It informed General Stuart that General Early would move upon York, Pa., and that he was desired to place his cavalry as speedily as possible with that, the advance division of Lee's right wing. The letter suggested that, as the roads leading northward from Shepherdstown and Williamsport were already encumbered by the infantry, the artillery, and the transportation of the army, the delay which would necessarily occur in passing by these would, perhaps, be greater than would ensue if General Stuart passed around the enemy's rear. The letter further informed him that, if he chose the latter route, General Early would receive instructions to look out for him and endeavor to communicate with him; and York, Pa., was designated as the point in the vicinity of which he was to expect to hear from Early, and as the possible (if not the probable) point of concentration of the army. The whole tenor of the letter gave evidence that the commanding general approved the proposed movement, and thought that it might be productive of the best results, while the responsibility of the decision was placed upon General Stuart himself. Well may General Longstreet say : " Authority thus given a subordinate general implies an opinion on the part of the commander that something better than the drudgery of a march along our flank might be open to him, and one of General Stuart's activity and gallantry should not be expected to fail to seek it." '
Having received his orders on the night of the 23d of June, General Stuart prepared on the 24th to execute them.]
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The right flank at Gettysburg: an account of General Gregg's Cavalry Command ... By William Brooke Rawle. 1878
[* There has existed a wide-spread supposition that Stuart, with his cavalry, was not even present at the battle of Gettysburg. This is partly owing to the fact that after the battles of Aldie and Upperville Stuart became separated from Lee's army, and was prevented from joining it, or from being of any assistance to its commander during its movements preceding the battle, by the interposition of Gregg's and Kilpatrick's cavalry. Stuart was thereby compelled to make a wide detour, only reaching Lee on the 2d of July, and owing to this separation and the loss of the " eyes and ears " of his army, Lee had, to a great extent, to move in the dark. To the fact of Stuart's absence from Lee's army many recent Confederate writers have attributed the results of the campaign, while others maintain that the two brigades under Generals Robertson and Jones, which did not accompany Stuart upon his independent movement, were amply sufficient for the purposes of observation.]
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Chancellorsville and Gettysburg by Abner Doubleday, 1882
[It seems strange that Lee should suppose that the Union army would continue inactive all this time, south of Washington, where it was only confronted by Stuart's cavalry, and it is remarkable to find him so totally in the dark with regard to Hooker's movements. It has been extensively assumed by rebel writers that this ignorance was caused by the injudicious raid made by Stuart, who thought it would be a great benefit to the Confederate cause if he could ride entirely around the Union lines and rejoin Lee's advance at York. He had made several of these circuits during his military career, and had gained important advantages from them in the way of breaking up communications, capturing despatches, etc. It is thought that he hoped by threaten ing Hooker's rear to detain him and delay his crossing the river, and thus give time to Lee to capture Harrisburg, and perhaps Philadelphia. His raid on this occasion was undoubtedly a mistake. When he rejoined the main body, his men were exhausted, his horses broken down, and the battle of Gettysburg was nearly over. As cavalry are the eyes of an army, it has been said that Stuart's absence prevented Lee from ascertaining the movements and position of Hooker's army. Stuart has been loudly blamed by the rebel chroniclers for leaving the main body, but this is unjust; Lee not only knew of the movement, but approved it; for he directed Stuart to pass between Hooker and Washington, and move with part of his force to Carlisle and the other part to Gettysburg. Besides, Stuart left Robertson's and Jones' brigades behind, with orders to follow up the rear of the Union army until it crossed, and then to rejoin the main body. In the meantime they were to hold the gaps in the Blue Ridge, for fear Hooker might send a force to occupy them. These two brigades, with Imboden's brigade, and White's battalion, made quite a large cavalry force: Imboden, however, was also detached to break up the Baltimore and Ohio Railroad to prevent forces from the West from taking Lee in rear; all of which goes to show how sensitive the Confederate commander was in regard to any danger threatening his communications with Richmond.]
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The Operations of the cavalry in the Gettysburg Campaign, by L. S. Trowbridge, 1893
[However such was his plan, and with that end in view General Early was ordered to York, Pa., ahd General Stuart was directed to place so much of his cavalry, as he should think best, as speedily as possible, in conjunction with that force which would constitute the right wing of the invading army.
To accomplish this, two plans were open to him; one, to pass along the flank of the army and cross the Potomac at Shepherdstown and Williamsport. That would seem to most military critics to have been the proper route, as he could then have kept constant watch on the movements of his enemy and maintained uninterrupted communication with his chief. But General Stuart conceived a more brilliant, if successful, and certainly much more hazardous plan, which was to pass around the rear of the Army of the Potomac. If this route afforded greater expedition in connecting with Early, and the tempting chance of capturing a train or some detached portions of the army, it also exposed him to the danger of being cut off from communication with his chief, and furnishing him with the information which it was of the highest importance tor him to have—a result which actually did occur through the quick movements and splendid fighting of the Union cavalry. Leaving Jones's and Robertson's brigades with the main army, he took with him the three brigades of Hampton and the two Lees for this perilous undertaking.
Doubtless he thought the brigades of Jones and Robertson with that of Jenkins, numbering altogether nearly 4,000 men, would be amply sufficient to keep Lee advised of all the movements of the Army of the Potomac. Perhaps they should have been, and it may be that it was not so much the absence of the three brigades of Hampton and the two Lees, as that of Stuart himself, that so disturbed General Lee. Certain it is that the absence of that officer was very sorely felt and greatly criticised. It has even been said that there was talk of a court martial for his disobedience of others, but that General Lee refused to order the court because, as he said. Stuart was allowed a discretion under his orders, and could not be tried for exercising that discretion.] (this suggestion of court martial is said to have come from the man who wrote the orders...Col. Marshall)
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Cavalry Studies From Two Great Wars, comprising The French Cavalry in 1870, by Lieutenant-Colonel Bonie. The German Cavalry in the battle of Vionville--Mars-la-Tour, by Major Kaehler. The operations of the Cavalry in the Gettysburg Campaign, by Lieutenant-Colonel George B. Davis, 1896.
[There was no time during the progress of the war when the approach of even an insignificant partisan force to the vicinity of the defenses of the Capital did not fully engage the attention and excite the alarm of the distinguished lawyer who then commanded the armies of the United States. If such an effect followed the incursion of a partisan force of less than a hundred men, why might not Stuart count upon a correspondingly increased effect to follow the news that he had interposed the greater part of his command between the Army of the Potomac and Washington. In this he was not mistaken, and General Lee so far concurred with him as to give him, upon certainly two occasions, written orders to carry the scheme into effect.]
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Then around 1920, all mention of Lee's orders to Stuart, and the 4,000 cavalry travelling with Lee, start to disapeer from popular history-- as does most of the Civil War until about 1960.
U.S. Army, The United States Infantry Association, 1922.
[The lack of sufficient Confederate cavalry was one of the determining factors in the Gettysburg campaign. Prior to the invasion of Maryland, Stuart, Lee's chief of cavalry, had proposed a raid around the Union army, upon the completion of which he would join the main body at Harrisburg. But when Lee learned at Chambersburg, May 28, that the Federal army had crossed the Potomac and that Meade was now in command, Stuart was crossing the same liver at Rowsers Ford. Without the eyes of his army, Lee was ignorant of the dispositions of the Federals. On May 30, General Hill, at Cashtown, sent Pettigrew's brigade to Gettysburg for the purpose of getting some shoes. Approaching that town, however, he saw a large body of Union cavalry, and retraced his steps several miles. Hill's interest and curiosity were aroused, so he sent forward Heth's division on the following morning. Hill found Bu ford's cavalry division drawn up on Seminary Ridge, west of town. He attacked at once, and thus, on his own initiative, not Lee's, the battle of Gettysburg was opened. Lee did not wish to fight Meade at Gettysburg, but his lack of cavalry prevented him from making the proper dispositions of his forces. Stuart did not join Lee until the second day of the battle, July 2, and then it was too late.]
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David Upton