In any case, I found this letter to be quite revealing, not only of Washington's diplomatic skills, but also of a surprising sense of humor he put to use to mute the "dressing down" he is giving to Sullivan.
Remember that Sullivan had already sent out some pretty snorty letters about 1) D'Estaing and 2) the French in general complaining about being left in the lurch at Rhode Island by our new allies. It was obvious that this letter was what Washington wrote to Sullivan at that point. I told Julien (the young Frenchman who is researching Lafayette's Farewell Tour route in New England) that in this letter Washington was telling Sullivan to "pipe down." (A bit tricky to explain that expression, but I think Julien got it.)
I don't usually think of Washington as being gifted in diplomacy, but please notice what he did in this letter. It is particularly impressive because Washington himself was probably very upset by the rift in the new alliance, which Sullivan had made even worse. As he says himself, "The disagreement between the army under your command and the fleet has given me very singular uneasiness." Nevertheless, Washington manages to give Sullivan a couple of "outs" before lowering the boom on his angry general.
1) First of all, he states that he has not heard from Sullivan since August 23, but says that Sullivan's messages must have gone astray.
2) Secondly, Washington says this of the French: "In our conduct towards them we should remember that they are a people old in war, very strict in military etiquette, and apt to take fire when others scarcely seem warmed." As you can see by the emboldened text, Washington makes a small joke implying that the French are overly touchy. In other words, he is suggesting that the French are so easily enraged that perhaps it is not completely Sullivan's fault that they are angry or offended.
Then, however, Washington goes on to make it clear that Sullivan must keep his mouth shut and do everything he can to keep the news of the "misunderstanding" between the French and Americans quiet.
"It is of the greatest importance, also, that the minds of the soldiers and the people should know nothing of the misunderstanding, or if it has reached them that ways may be used to stop its progress and prevent its effects."
How thrilling it was to read the actual words written by Washington, and to see his diplomacy (and possibly his sense of humor) at work!
To Major General John Sullivan
Head Quarters White plains 1st Septr 1778.
The disagreement between the army under your command and the fleet has given me very singular uneasiness. The Continent at large is concerned in our cordiality, and it should be kept up by all possible means that are consistent with our honor and policy. First impressions, you know, are generally longest remembered, and will serve to fix in a great degree our national character among the French. In our conduct towards them we should remember that they are a people old in war, very strict in military etiquette, and apt to take fire when others scarcely seem warmed. Permit me to reco⟨mmend⟩ in the most particular manner, ⟨ the ⟩ cultivation of harmony and go⟨od⟩ agreement, and your endeavours to ⟨des⟩troy that ill humour which may ⟨have⟩ got into the officers. It is of the greatest importance, also that the minds of the soldiers and the people should know nothing of the misunderstanding, or if it has reached them that ways may be used to stop its progress and prevent its effects.
I have received from Congress the inclosed by which you will perceive their opinion with regard to keeping secret the protest of the General Officers I need add nothing on this subject.
I have one thing however more to say—I make no doubt but you will do all in your power to forward the repairs of the french fleet, and in rendering it fit for service, by your recommendations for that purpose to those who can be immediately instrumental. I am Dr Sir your most Obt hble servt