George Washington's letter, dated 14 December 1782, to Jean B. Donatien de Vimeur, Comte de Rochambeau: from
The Writings of George Washington from the Original Manuscript Sources, 1745-1799. John C. Fitzpatrick, Editor. Taken from Library of Congress online website.
Newburgh, December 14, 1782.
I cannot, My dear Genl., permit you to depart from this Country without repeating to you the high sense I entertain of the Services you have rendered America, by the constant attention which you have paid to the Interests of it. By the exact order and discipline of the Corps under your Command, and by your readiness, at all times, to give facility to every measure which the force of the Combined Armies was competent to.
To this testimony of your Public character I should be wanting to the feelings of my heart, was I not to add expressions of the happiness I have enjoyed in your private friendship. The remembrance of which, will be one of the most pleasing Circumstances of my life.
My best wishes will accompany you to France, where I have no doubt of your meeting the Smiles and rewards of a generous Prince; and the warmest embraces of Affectionate friends.  I have the honor etc. 
[Note 37: The draft, which is also in the writing of Washington, has at this point: "sincerely hope and."]
[Note 38: The draft has at this point: "Adieu."]
[Note 39: From the letter sent in the Rochambeau Papers in the Library of Congress.]
Washington's Biographer's Tribute to Rochambeau is presented in an artilce: "How a Great Historian Studied a Great American," American Heritage, February 1956, pp. 69 and 70. The article quotes from Douglas Southall Freeman's letters to the Carnegie Corporation and addresses his research on George Washington. Portions of the article are quoted below; text inside brackets has been inserted by this webpage editor.
Letter dated January 4, 1952 [written upon ending volume V]
"He [Rochambeau] is surely a symbol of Franco-American accord as Lafayette ever was-and was self-effacing. Lafayette was not."
... "It may be doubted whether there was a time, prior to the summer of 1781, when it could be said with reasonable certainty that the continental cause would survive for six months longer. To what did it owe its continued, if precarious, existence? Beyond all doubt, to the example and character of Washington more than to any single influence."
[Freeman goes on to explain the crucial allied campaign of Yorktown and the vital French role]
"After struggling for months with the ugly detail of administration and camp diplomacy, it has been a great delight to turn to Yorktown as a full campaign, ready set, as it were, for detailed study according to the new techniques.... I would not ask for one [military campaign] more interesting. It is a textbook model in the relationship of allies and, above all, in concentration."
"How strange that these two aspects of the operations of August-October, 1781, have received so little attention! Thanks to Rochambeau, the resources of the French engineering and artillery staffs were placed at Washington's disposal completely and unostentatiously. Few jealousies were aroused, while the French did brilliantly several things the inexperienced Americans scarcely would have been able to do at all."
"This was particularly true of the running of the first and second 'parallels', as the siege trenches were styled. Washington matched this with a concentration that ranks with the best Eighteenth-Century achievements of logistics, though Washington himself would not have understood what we mean by that over-whipped word. He hear on the fourteenth of August, 1781, when he was on the Hudson, that De Grasse's fleet was coming to Virginia. One month later, to the very day, Washington rode into Williamsburg in the knowledge that Barras' French squadron from Newport, the French garrison of that base, all their siege guns, the army of Rochambeau from the New York front, an American detachment of 2,000 men and the baggage of the Franco-American forces were moving toward him. Before the end of September, Washington had all these troops and most of this equipment in hand, and began his advance on the works of Cornwallis at Yorktown. He used every means of transportation he could find and he somehow was able to co-ordinate them. The Revolution produced nothing more remarkable."
Letter dated September 15, 1952 [still addressing volume V, which was just printed]
[first feature of volume V is that evidence shows] "... that the winter of 1779-80 at Morristown and Jockey Hollow was a period of far worse suffering than the corresponding months of 1777-78 at Valley Forge."
"The great adventure of co-operation with the French is a second feature of Volume V. An unhappy adventure it was at the outset! Worse bungling than that of Major General John Sullivan in dealing with Comte d'Estaing, the French naval commander, would be difficult to find. [One could also add the disaster of d'Estaing at Savannah in 1779] After the coming of Rochambeau, co-operation was easier in every way. All that I suggest in my report of January 4 [see prior letter] concerning this great French soldier had been confirmed by a review of the evidence. Rochambeau should stand second only to Lafayette among the Frenchmen of the Revolution era to whom the American people are indebted...."