The harbor of Tripoli lies in a shallow indentation of the coast, being tolerably protected against easterly and westerly gales by the formation of the land, while a reef of rocks, which stretches for a mile and a half in a northeasterly course, commencing at the town itself, breaks the seas that roll in from the northward. This reef extends near half a mile from the walls, entirely above water, and is of sufficient height and width to receive water batteries, containing the Lazaretto and one or two forts. It is this commencement of the reef which constitutes what is usually termed the mole, and behind it lies the harbor proper. At its termination is a narrow opening in the reef which is called the western entrance, through which it is possible for a ship to pass, though the channel is not more than two hundred feet in width. Beyond this passage the rocks reappear, with intervals between them, though lying on shoals with from one and a half to five and a half feet of water. The line of rocks and shoals extends more than a mile outside of the western entrance. Beyond its termination is the principal entrance to Tripoli, which is of sufficient width though not altogether free from shoals. The distance across the bay, from the northeastern extremity of the rocks to what is called the English fort, on the main land, is about two thousand yards, or quite within the effective range of heavy guns. In the bottom of the bay, or at the southeastern angle of the town, stands the bashaw’s castle, a work of some size and force. It lies rather more than half a mile from the western entrance, and somewhat more than a mile from the outer extremity of the reef. Thus any thing within the rocks is commanded by all the water defences of the place, while shot from the castle, and more especially from the natural mole, would reach a considerable distance into the offing. Some artificial works aided in rendering the northwestern corner of the harbor still more secure, and this place is usually called the galley mole. Near this is the ordinary landing, and it is the spot that may properly be termed the port.
The Tripolitans fully expected the attack of the 2d of August, though they little anticipated its desperate character, or its results. They had anchored nine of their large, well-manned gunboats just outside of what are called the Harbor Rocks, or the northeastern extremity of the reef, evidently with a view of flanking the expected attack on the town, which, lying on the margin of the sea, is much exposed, though the rocks in its front were well garnished with heavy guns. Accustomed to cannonading at the distance of a mile, these gunboats expected no warmer service, more especially as a nearer approach would bring their assailants within reach of the castle and batteries. In addition to the nine boats to the eastward, there were five others which also lay along the line of rocks nearer to the western entrance, and within pistol shot of the batteries in that part of the defences. Within the reef were five more gunboats and several heavy galleys, ready to protect the outer line of gunboats at need, forming a reserve.
Com. Preble had borrowed only six gunboats from the King of Naples, and these were craft that were much inferior in size and force to the generality of those used by the enemy. Each of these boats had a few Neapolitans in her to manage her on ordinary occasions, but, for the purposes of action, officers and crews were detailed from the different vessels of the squadron. These six boats were divided into two divisions; to the command of one was assigned Lieut. Com. Somers, while Lieut. Com. Decatur led the other. Somers was thought to be the senior lieutenant of the two, though Decatur was at this time actually a captain, and Somers himself was a master commandant; as well as Stewart, Hull and Smith, though the intelligence of these promotions had not yet reached the squadron. The three boats commanded by Somers were
No. 1. Lieut. Com. Somers, of the Nautilus.
No. 2. Lieut. James Decatur, of the Nautilus.
No. 3. Lieut. Blake, of the Argus.
Decatur had under his immediate orders,
No. 4. Lieut. Com. Decatur, of the Enterprise.
No. 5. Lieut. Joseph Bainbridge, of the Enterprise.
No. 6. Lieut. Trippe, of the Vixen.