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It was engaged at Port Gibson where the brigade commander fell, and it lost heavily there in killed, wounded, and captured.
http://www.mycivilwar.com/regiments/csa-al/al_inf_23_reg.htm
You can gain an understanding of the battle through Warren E. Brabau's "Ninety-Eight Days, A Geographer's View of the Vicksburg Campaign, which contains five maps of the battlefield area.
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THE TWENTY-THIRD ALABAMA INFANTRY.
This regiment was armed by private enterprise and organized at
Montgomery in November, 1861.
It first served at Mobile and then in the Kentucky campaign. It
took a prominent part at Port Gibson, May 1, 1863, and lost
heavily; was at Baker's Creek, May 16th; at Big Black, May 17th;
and served in the trenches during the siege of Vicksburg, May
18th to July 4th.
It joined the army of Tennessee in October, 1864, and fought at
Lookout Mountain and Missionary Ridge, November 23rd to 25th; was
with Johnston in his campaign in Georgia in 1864, and suffered
very heavily at Jonesboro; was with Hood in Tennessee, and did
splendid service in covering the retreat of Hood's army from
Nashville.
The regiment last won distinction at Bentonville, March 19-21,
1865.
Capt. John Stevens was killed at Port Gibson, Col. Franklin K.
Beck at Resaca, Maj. A. C. Roberts at New Hope, Capt. F.
Butterfield at Atlanta, and Captain Rutherford at Jonesboro.
Other field officers were Col. Joseph B. Bibb and Majs. Felix
Tait, Francis McMurray, John J. Longmire, G. W. Mathieson and
James T. Hester.
Source: Confederate Military History, vol. VIII, p. 129
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The Regiment arrived at Vicksburg, Mississippi on January 1, 1863, too late to participate in the repulse of General Sherman's Army at the Battle of Chickasaw Bayou. However, upon their arrival, General S.D. Lee ordered the Regiment, along with the 2nd Texas, 3rd Tennessee, and 30th Tennessee Infantry Regiments, to pursue the beaten Federal army back to their transports on the Yazoo River. 10 Following that victory, the 23rd Alabama, along with the other regiments of Tracy's brigade, occupied defenses near Snyder's Bluff, Mississippi.11 Lieutenant General Pemberton shifted Tracy's Brigade south to Warrington, Mississippi in March, 1863 in response to General Grant's southward movement past Vicksburg to Hard Times on the Louisiana shore.12
On May 1, 1863, the Regiment participated in the Battle of Port Gibson, Mississippi against General Grant's Army. In this battle, General Tracy's Brigade, numbering 1,516 soldiers, was assigned to General Bowen's Division. General Bowen had about 5,500 men engaged against roughly 23,000 Union troops.13
Tracy's Brigade moved from Warrington, Mississippi, by a forced march of about 30 miles, on April 29-30, 1863, to join General Green's Brigade at Port Gibson. The Regiment "...arrived, jaded from a forced march and without provisions. I [General Bowen] ordered them to halt near town, to collect stragglers, cook rations, and after a short rest to report to [General] Green, who would point out their position." 14
The Federal army began their attack about 1 a.m. on May 1, 1863, and by 8 a.m., the Confederate left flank under General Green was in trouble. General Bowen directed General Tracy to reinforce General Green. General Tracy ordered the 23rd Alabama and his artillery battery to move to Green's assistance. Immediately upon their arrival, General Bowen ordered the 23rd Alabama to support the 6th Mississippi Regiment and an Arkansas regiment, in charging an artillery battery to relieve the pressure on his left flank. "I called upon the Sixth Mississippi to charge a battery in front of them, to which they nobly responded, and were well seconded by the Twenty-third Alabama on their right, but not by the Arkansas troops, to their left." 15 These two regiments held this position for about an hour before being forced back to their starting positions.16
General Bowen gave his troops the order to retire from the battlefield about a half hour before sundown. The Twenty-third Alabama Infantry , still with General Green's forces, was among the first to leave. The rest of General Tracy's Brigade, now under command of Colonel Garrott due to General Tracy's death, followed General Green's Brigade to Grand Gulf, Mississippi.17
http://www.canerossi.us/23ala/part1.htm
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May the 8 1863
Camp Near Vicksburg.
Dear Sister I seat my self to let you know that I am as well as usual hoping when this little message come to hand it may find you enjoying the Same good blessings of life I have no news of importance to write I reckon you have heard of the fight the Ala 23 has been long hunting and at last we found it and I tell you it was a hot one I Saw many fall and heard many crys & grons of the dying and wounded but the Lord was good and merciful to me even a ball did not touch my clothes though they were flying around me and many fell on every Side
Private M.L. Calk enlisted in Company K of the Twenty-Third Alabama
http://www.canerossi.us/23ala/calk.htm