Williams'-Hoxton's-Tobin's Battery [also called Memphis Light Artillery] completed its organization in July, 1861, at Memphis, Tennessee. It moved to Camp Beauregard, Kentucky and reported 2 officers and 43 men present for duty. Later the company fought at Farmington and Corinth, then was assigned to the Department of Mississippi and East Louisiana. It was active in the Vicksburg operations and captured on July 4, 1863. Exchanged in October, its 28 men were sent to Mobile. Here the unit served until the end of the war. It was included in the surrender on May 4, 1865.
http://www.itd.nps.gov/cwss/regiments.cfm
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CAPTAIN THOMAS F. TOBIN'S TENNESSEE LIGHT ARTILLERY COMPANY
Also called Memphis Light Battery-Tobin's Horse Artillery
. . . It then moved to Holly Springs, to Lumpkin Mills, to Abbeville, to Grenada, and from Grenada moved by rail to Vicksburg, where it arrived January 1, 1863. On September 25, 1862, a detachment from the 2nd Alabama Artillery Battalion was temporarily attached to the battery and remained with it until after the fall of Vicksburg, July 4, 1863. During the Vicksburg campaign one section* of the battery was stationed for awhile at Snyder's Bluff, one section at Chickasaw Bluffs. The two sections united at Haynes Bluff on March 13, and moved by the steamer Alagnolia to Yazoo City, Mississippi, on March 20, where the battery manned two 20-pounder Parrott guns. It moved to Fort Pemberton March 28, back to Haynes Bluff April 20, from there to Warrenton, where it did picket duty from May 3 to 17. From that time on it was in the center line of the fortifications at Vicksburg until the surrender. . . .
http://www.tngenweb.org/civilwar/csaart/tobin.html
* A section consists of two guns. Normally, in a six gun battery, they would sometimes be broken into two gun sections and separated.
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During the Vicksburg siege, they were assigned to Moore's Brigade, Forney's Division. They could have been anywhere on Moore's line of entrenchments from the Great Redoubt on the Jackson Road, to the Railroad Redoubt, just South of Baldwin's Ferry Road, May 17 to July 4, 1863