Soon after the affair of the persecuted Waldenses was concluded the Protector formed an alliance, offensive and defensive, with the French, in which it was agreed that Dunkirk should be delivered up to him. In consequence of this agreement six thousand men were sent over to join the French army, and Peters received a commission to attend them thither. The town of Dunkirk, in consequence of this league, was taken from the Spaniards, and on the 26th of June, 1658, was delivered to Colonel Lockart, Cromwell's ambassador at the French Court. Lockart wrote the following letter to Secretary Thurloe:-- "DUNKIRK, _July_ 8-18_th_, 1658. "May it please your Lordship, "I could not suffer my worthy friend, Mr. Peters, to come away from Dunkirk without a testimony of the great benefits we have all received from him in this place, where he hath laid himself forth in great charity and goodness in sermons, prayers, and exhortations, in visiting and relieving the sick and wounded; and, in all these, profitably applying the singular talent God hath bestowed upon him to the chief ends, proper for an auditory. For he hath not only showed the soldiers their duty to God, and pressed it home upon them, I hope with good advantage, but hath likewise acquainted them with their obligations of obedience to his Highness's government and affection to his person. He hath laboured amongst us here with such goodwill, and seems to enlarge his heart towards us, and care of us for many other things, the effects whereof I design to leave upon that Providence which has brought us hither.... Mr. Peters hath taken leave at least three or four times, but still something falls out which hinders his return to England. He hath been twice at Bergh, and hath spoke with the Cardinal (Mazarin) three or four times; I kept myself by, and had a care that he did not importune him with too long speeches. He returns, loaden with an account of all things here, and hath undertaken every man's business. I must give him that testimony, that he gave us three or four very honest sermons; and if it were possible to get him to mind preaching, and to forbear the troubling himself with other things, he would certainly prove a very fit minister for soldiers. I hope he cometh well satisfied from this place. He hath often insinuated to me his desire to stay here, if he had a call. Some of the officers also have been with me to that purpose; but I have shifted him so handsomely as, I hope, he will not be displeased. For I have told him that the greatest service he can do us is to go to England and carry on his propositions, and to own us in all other interests, which he hath undertaken with much zeal."