Sir--I have the honor to inform you that I departed from this city on the 11th June, accompanied by Col. Ross, with a detachment of seventy of the 44th regiment of infantry. On the 12th, reached the schooner Carolina, of Plaquemine, and formed a junction with the gun vessels at the Balize on the 13th, sailed from the southwest pass on the evening of the 15th, and at half past 8 o'clock, A.M. on the 16th, made the Island of Barrataria, and discovered a number of vessels in the harbor, some of which shewed Carthagenian colors. At 2 o'clock, perceived the pirates forming their vessels, ten in number, including prizes, into a line of battle near the entrance of the harbor, and making every preparation to offer me battle. At 10 o'clock, wind light and variable, formed the order of battle with six gun boats and the Sea Horse tender, mounting one six pounder and fifteen men, and a launch mounting one twelve pound carronade; the schooner Carolina, drawing too much water to cross the bar. At half past 10 o'clock, perceived several smokes along the coasts as signals, and at the same time a white flag hoisted on board a schooner at the fort, an American flag at the mainmast head and a Carthagenian flag (under which the pirates cruise) at her topping lift; replied with a white flag at my main; at 11 o'clock, discovered that the pirates had fired two of their best schooners; hauled down my white flag and made the _signal for battle_; hoisting with a large white flag bearing the words "Pardon for Deserters"; having heard there was a number on shore from the army and navy. At a quarter past 11 o'clock, two gun boats grounded and were passed agreeably to my previous orders, by the other four which entered the harbor, manned by my barge and the boats belonging to the grounded vessels, and proceeded in to my great disappointment. I perceived that the pirates abandoned their vessels, and were flying in all directions. I immediately sent the launch and two barges with small boats in pursuit of them. At meridian, took possession of all their vessels in the harbor consisting of six schooners and one felucca, cruisers, and prizes of the pirates, one brig, a prize, and two armed schooners under the Carthagenian flag, both in the line of battle, with the armed vessels of the pirates, and apparently with an intention to aid them in any resistance they might make against me, as their crews were at quarters, tompions out of their guns, and matches lighted. Col. Ross at the same time landed, and with his command took possession of their establishment on shore, consisting of about forty houses of different sizes, badly constructed, and thatched with palmetto leaves.