On the 18th of June the squadron was assembled just below Vicksburg, having in company also seventeen schooners of the mortar flotilla, still under Porter's command. These were placed as rapidly as possible in suitable positions on the two sides of the river, opened fire on the 26th, and continued it through the 27th. Upon the evening of the latter day Porter notified the flag-officer that he was ready to cover, by a steady bombardment, the intended passage of the fleet before the batteries. [Illustration: PASSAGE OF VICKSBURG BATTERIES, JUNE 28, 1862. ORDER OF ATTACK.] Vicksburg is situated on the first high land met on the east bank of the Mississippi after leaving Memphis, from which it is four hundred miles distant. The position was one of peculiar strength and importance for commanding the navigation of the river. Not only was it exceptionally lofty, and on one flank of that series of bluffs which has before been mentioned as constituting the line upon which the Confederate grip of the stream was based, but the tortuous character of the channel gave particular facilities for an enfilading fire on vessels both before and after they came abreast the works. They were thus exposed to a longer and more dangerous cannonade than is the case where the stream flows straight past the front of a battery. The channel has now changed; but in 1862 the river, which from Memphis had pursued its winding course through an alluvial country, made when abreast of Vicksburg a sharp turn to the northeast, as though determined to reach the bluffs but four miles distant. As it neared them it swung round with a sharp turn to the southwest, parallel to its recent direction, flowing for the most part close to the foot of the hills. Between the two reaches, and formed by them, immediately opposite the town, there was a low tongue of land, or promontory, four miles long and less than one wide. The squadron, being below, had to steam up through the lower reach against the current, make the sharp turn at the bend, and then pass through the upper reach. In the bend it was followed by a fire from the highest part of the bluffs, to which it could make no reply.