I will take a shot at trying to answer your questions.

Grant opened his failed first Vicksburg Campaign in early 1863. I have a notation that the 1st Texas Legion (27th Texas Cavalry) was part of this battle from February 16 to the 20th. I am having trouble finding how,where and what they did.
The 27th suddenly left this action, maybe after the erection of Ft Pemberton and raced to Tennessee to fight in the Battle of Thompson Station on 5 March 1863. They did not stay for the end of the First Vicksburg Campaign.

I can find nothing to substantiate the presence of the 27th Texas Cavalry during the Yazoo River operations Feb 16-20. 1863. All of my information points to this regiment leaving Mississippi in Feb 1863 as part of the Texas Brigade with Van Dorn. They would have been hard pressed to travel from the Yazoo River area of Mississippi in time to fight in the March 5th, 1863 battle of Thompson Station in Williamson County, Tennessee, near Franklin-well over 300 miles away.

Does anyone have any data on units involved in Pemberton's efforts to stop this thrust by Grant and maybe the actions of the 27th Texas Cavalry?

CAMP PEMBERTON, Yazoo River, February 21, 1863.
Lieutenant-General PEMBERTON,
Commanding, &c.:
GENERAL: Upon my arrival here to-day, I found that Major [M.] Meriweather had, in accordance with my instructions, acted promptly in his selection of a place where we may be enabled to construct suitable works for the defense of this river. He has chosen this point [Beck's Ferry], and vigorously commenced the erection of works which I trust, when completed, will do much toward preventing the passage down of the enemy. The location is 2 1/2 miles by land and about 4 by water below Greenwood. The banks are some 8 feet above water, and the guns will be mounted upon works constructed of earth and cotton bales, so as to place them at an altitude that insures a plunging fire upon the enemy's boat. The Tallahatchee and the Yazoo Rivers are only about 500 yards apart here, and the works commanding each will be connected by suitable lines of intrenchments. Colonel [T. N.] Waul with his troops is encamped here. He is judicious in his arrangements, and I would recommend that he be kept in command of this position.
The river here will also be obstructed with rafts, if it can be done before the enemy approach. This is highly probable, as there is not the least apparent prospect of their speedy descent, and no present indication of a further rise in the river. If, however, the obstruction by rafts cannot be completed in time, I shall use the C. S. S. Star of the West, as stated in my last dispatch, and, if necessary, sink her athwart the channel.
I would remove the two pieces sent by you to Yazoo City, but do not think it best to do so unless others could be sent there. That position, naturally strong, should be kept in a condition of defense in the event we should be compelled to abandon the works up the river.
I have given orders that those boats now being used for the transportation of supplies on the Tallahatchee and Yalabusha Rivers for Grenada, and on the Yazoo for Vicksburg, shall not be interfered with, and to this end the rafts which I have spoken of will not be placed in position to obstruct the streams until threnders it absolutely necessary to do so. Those boats not in use for this purpose are now being encircled with cotton bales, under the direction of Captain [I. N.] Brown, who will command them, and assist our works by boarding the enemy if he should attempt a descent of the river.
I have issued an order to Colonel [R.] McCulloch to hold his cavalry in readiness to march in the direction of the Coldwater, if a practicable road can be discovered.
Colonel Waul has established a line of couriers between this point and Vaiden, on the Central Railroad, through which channel communication with headquarters may be conveniently held.
I inclose you a rough sketch of the position here. * That portion in ink will represent the works that are being constructed. Colonel Waul will send you a more accurate sketch of the river and works as soon as the engineer can prepare it for you.
Will go up the Tallahatchie to-morrow in the direction of the Coldwater, with the view of finding some other suitable points for the erection of works or obstruction of the streams, proceeding up the Coldwater toward the Yazoo Pass. My progress up the latter, however, will depend entirely upon the information I may be enabled to obtain respecting the strength of the enemy.
Very respectfully, your obedient servant,
W. W. LORING.

HEADQUARTERS FORT PEMBERTON,
Near Greenwood, MISS., March 22, 1863
MAJOR: I beg leave to submit the following report of operations on the Yazoo and Tallahatchie Rivers:
In accordance with your instructions, I left Jackson, Ms., on the morning of February 17 last, with the view to finding some suitable place on the Yazoo or Tallahatchie whereat to erect works and place obstructions to the passage down of the enemy.

…At 4 o'clock in the afternoon the fight was resumed by another gunboat, which we supposed to be the iron-clad De Kalb. After two hours hard fighting, the boat withdrew. During the day, Colonel
[T. N.] Waul, commanding post, sent out a detachment of his Legion as skirmishers, who engaged a large body of the enemy's infantry and cavalry and drove them back to their transports.
…While I am thankful for the perfectly successful result of our labors here, I wish to express mu obligations to Colonel T. N. Waul, Texas Legion, for his energy, promptness, and good judgment in the discharge of his duty with his Legion in the fortifications during the engagements. I was greatly indebted to him for the assistance he rendered on so many occasions, and which contributed to our frequent successes.
Colonel Ashbel Smith, commanding SECOND Texas, in charge of the right of our defenses, with great gallantry and skill prevented the enemy turning that flank.
Lieutenant Colonel W. N. Brown, commanding Twentieth Mississippi, and Captain H. Cantey, also of the Twentieth, for important aid in collecting material for our raft while in readiness to defend the works.
Colonel D. R. Russell, Twentieth Mississippi during the last engagement, and General Tilghman subsequently (though the enemy was still I our front), rendered every possible aid. The general, in command of our left flank, kept the enemy apprehensive of their rear…
W. W. LORING,

Another question about S.D Lee. Was he involved in the above

S D Lee volunteered to lead a force against the next & most extraordinary of Grant’s attempts to reach Vicksburg –the Steele’s Bayou Expedition, called the Deer Creek Expedition by the Confederates…Porter…flotilla ran into Steele’s Bayou on March 16, 1863.

REPORT 16
Report of Maj. Gen. Carter L. Stevenson, C.S. Army, commanding District.
HEADQUARTERS SECOND DISTRICT
DEPARTMENT MISSISSIPPI AND EAST LOUISIANA
Vicksburg, March 29, 1863

MAJOR: I have the honor to report that, on the evening of the 20th instant, I received information that the enemy were endeavoring to turn my right by an expedition, which, entering Steele’s, passed into Black Bayou and Deer Creek, and was at the time that the intelligence reached me within 20 miles of Rolling Fork, through which they expected to make their way into the Sunflower River and thence into the Yazoo.

The expedition consisted of five iron-clad boats, three armed sternwheel boats, four transports, three tugs, and nine barges, all heavily laden with troops. The importance attached to it by the enemy may be estimated by the fact that the boats were commanded by Acting Rear-Admiral Porter and the troops by General Sherman.

Some time before, I had sent off sharpshooters, under the command of Major (H.W.) Bridges, with orders to report to Colonel Ferguson, and co-operate with him in protecting the country drained by Deer Creek and the Sunflower from the raids of the enemy. This command reported to him on the 16th instant.

As soon as possible after the receipt of the intelligence, I directed Major-General Maury, commanding the right wing, to send Brigadier-General Featherston’s brigade to Rolling Fork, to check their farther advance, and immediately afterward to dispatch a force, under Brigadier-General Lee, with order to make their way up Deer Creek, fortify and obstruct it at the high ground at Hardee’s, and cut off, if possible, the retreat of the enemy.

The attack made upon them by our forces in front was successful. They were repulsed in confusion, with a loss of some camp and garrison equipage and several fine barges on the first day, and, being closely followed up subsequently, were steadily driven back, and, at last, completely foiled, relinquished their attempt, and, returning, resumed their former position in front of the city on the evening of the 27th instant.

The damage done their boats was so great that it could easily be discovered from the lookout station at this point.

I regret that not even the energy of General Lee, who generously volunteered for the occasion, could overcome the difficulties in his way in time to intercept their retreat. Had it been possible, he would have done it.

For notices of subordinate commanders, I refer you to the report of Major-General Maury, herewith inclosed, and the letters of Colonel Ferguson, heretofore forwarded.

I am, major, respectfully, your obedient servant,
C.L. STEVENSON
Major-General, Commanding.
Maj. R.W. MEMMINGER,

A.A.G., Dept. of Mississippi and East Louisiana, Jackson

REPORT 17
Report of Maj. Gen. Dabney H. Maury, C.S. Army, commanding Division.
HEADQUARTERS MAURY’S DIVISION
Vicksburg, March 27, 1863

MAJOR: I have the honor to report that the expedition under General Sherman and Admiral Porter, which endeavored to penetrate, by way of Steele’s Bayou, Deer Creek, Rolling Fork, and Sunflower River, into Yazoo River, has been defeated and driven back. Colonel Ferguson now occupies Black Bayou, and has established communication with General Lee at Lower Deer Creek.

So soon as I was informed of this movement of the enemy, I ordered General Featherston to proceed with a portion of his brigade to re-enforce Colonel Ferguson, and to assume command of his forces. I also gladly availed myself of General Lee’s offer to conduct a force from Haynes’ Bluff up Lower Deer Creek, and ordered him to attack, if possible, the enemy on Black Bayou. These measures have resulted in the complete defeat of the enemy.

I cannot too highly commend Colonel Ferguson’s energy and daring. To his prompt soldiership we are indebted for the arrest of the progress of the expedition until such re-enforcements came to him as have enabled us to defeat it. He has been in the advance all the time, continually pressing the enemy back. His only fear has been lest the enemy should escape.

It is again my pleasure to call to your favorable notice Brig. Gen. S.D. Lee, who volunteered to conduct a force by Lower Deer Creek to Black Bayou, and has been most energetic overcoming the difficulties of that route. The enemy retreated before General Lee could reach him.

Not having yet received General Featherston’s complete report of his operations, I have nothing more to add at this time.
DABNEY H. MAURY,
Major-General

Surely after 149 years, you guys have resolved the campaigns, but apparently not. For I have now read 3 versions.

On the Texas board, it was noted that VNMP Vicksburg Order of Battle Had only Two regiments at Yazoo Pass and The 1st Texas Legion (aka the 27th Texas Cavalry Regiment) was not listed.

Waul's Texas Legion was listed, and I am betting that the 27th was the Legion there and VNMP made another mistake, as they did on Bridge's Arkansas Battalion, which was made up of two Texas and one Missouri Cavalry Companies. The two Texas Companies were from Waul's Regiment

I am trying to locate one 12 Company regiment from the 15 to the 20th of February, 1863. This unit had participated in the Holly Springs Raid.
Earl Vam Dorn was moving his Corps to Tennessee. This one regiment has a report of one battle in the time frame stated at Yaxoo Pass.

Waul’s Legion is reported by multiple sources as being in the Yazoo operations beginning Feb 16, 1863. And, so is Bridge’s Battalion

My question is what did the 27th do at Yazoo Pass from the 16th to the 20th. That they were there comes from the National Archives… This one regiment has a report of one battle in the time frame stated at Yaxoo Pass.

Can you share the battle report of the 27th and ID the specific NARA source which places it there at that time?