First of two battles to open the Tennessee River to Union transportation of men and supplies.
For information on Grant's progressively higher ranks as he achieved victory after victory, see the link below on his ranks and promotions.
How many soldiers make up a Company, a Regiment, a Brigade, a Division and a Corps? How did Grant serve at each level? See the Union Army Organization link below.
The military attire of Grant during the Civil War tells you something about his rank.
1861 June Colonel 21st Illinois volunteers. Eagle on his shoulder. Buttons in groups of 2.? Not sure.
Single Star on his shoulders, August, 1861, Brigadier General of Volunteer Soldiers. Buttons in groups of 2.
Two Stars on his shoulders, February, 1862, Major General of Volunteer Soldiers. Buttons in groups of 3.
Two Stars on his shoulders, Post-Vicksburg Victory, Major General, Regular Army. Buttons in groups of 3.
Three Stars on his shoulders, March 9, 1863, Lieutenant General all Union Armies. Buttons in groups of 3.
Four Stars on his shoulders, July, 1866, General of all the Armies. Buttons in groups of 4.
Article from Civil War Times (undated) on the American Battlefield Trust website. Grant at Ft. Donelson and how he came to be called "Unconditional Surrender Grant."
Was Grant Drinking at Shiloh? Absolutely not!
William R. Rowley, on Grant's staff and in the field with him at Shiloh had this to say about Grant's presumed inebriation during the first day's battle. This letter was subsequently forwarded to Representative Elihu B. Washburne.
Head Quarters Army in the Field
Near Pittsburg Tenn, April 19th 1862
E Hempstead Esqr
... I pronounce it an unmitigated slander. I have been on his Staff ever since the Donelson affair (and saw him frequently during that) and necessarily in close contact with him every day, and I have never seen him take even a glass of liquor more than two or three times in my life and then only a single at a time. And I have never seen him intoxicated or even approximate to it. As to the story that he was intoxicated at the Battle of Pittsburg, I have only to say that the man who fabricated the story is an infamous liar, and you are at liberty to say to him that I say so. ...
Yours &c W R ROWLEY