Michael George 'Mike' KOEHLER and his younger brother George Michael KOEHLER both served in Company B of the 17th Regiment, Iowa Volunteer Infantry.The regiment was mustered into service April 16, 1862, and mustered out on July 25, 1865

  "The 17th was mustered into service April 16, 1862 at Keokuk under the leadership of Colonel John W. Rankin, Lieutenant Colonel David B. Hillis, and Major Samuel M. Wise. This regiment served at Iuka, Corinth, and Vicksburg. At Iuka, where all the superior officers were disabled, command was assumed by a captain. Though the battle was not immediately decisive, the Confederate forces retreated during the following night so that the Union forces were victorious, but the loss of Iowa men was great". --- Quoted from 'Iowa in Times of War', by Jacob A. Swisher.

  The two 'KAHLER' brothers and the 17th also took part in the 'Third Battle of Chattanooga', Tennessee, near the north Georgia border and fought there in the Battle of Missionary Ridge, Nov. 25, 1863 as Union General Sherman worked his way south into Georgia and commenced his 'March to the Sea'.
  George was slightly wounded, and 'Mike' went 'missing in action' (captured there, as it turned out).   http://www.civilwarhome.com/chattannoga.htm

The Order of Battle showed
SEVENTEENTH ARMY CORPS.

SECOND DIVISION.
Brig. Gen. JOHN E. SMITH.
Second Brigade.
Col. GREEN B. RAUM.
Col. FRANCIS C. DEIMLING.
Col. CLARK R. WEVER.
including among the companies thereto attached,
17th Iowa:
    Col. Clark R. Wever.
    Maj. John F. Walden.
10th Missouri:
    Col. Francis C. Deimling.
    Lieut. Col. Christian Happel.
24th Missouri, Company E, Capt. William W. McCammon.
80th Ohio, Lieut. Col. Pren Metham.
             
                                                            -------
  Speaking of MILITARY SERVICE, I present this quote from the 'Roster and Record of Iowa Troops In the Rebellion, Vol. 3', by Guy E. Logan http://iagenweb.org/civilwar/books/logan.htm

HISTORICAL SKETCH
SEVENTEENTH REGIMENT IOWA VOLUNTEER INFANTRY,
Co. B...
Kahler, George.* (Veteran.) Age 18. Residence Nauvoo, Ill., nativity Bavaria.
Enlisted March 3, 1862.
Mustered March 25, 1862.
Wounded slightly Nov. 25, 1863, Missionary Ridge, Tenn.
Reenlisted and re-mustered April 22, 1864.
Taken prisoner Oct. 13, 1864, Tilton, Ga. [injured in a collapsed blockhouse under Confederate mortar attack]
Mustered out May 26, 1865, Davenport, Iowa.
[Must be George Michael]

Kahler, George M.* Age 22. Residence Nauvoo, Ill., nativity Bavaria.
Enlisted March 6, 1862.
Mustered March 25, 1862.
Promoted Sixth Corporal March 1, 1863;
Fourth Corporal April 1, 1863.
Missing in action Nov. 25, 1863, Missionary Ridge, Tenn.
Mustered out April 15, 1865, Davenport, Iowa, expiration of term of service.
[Must be Michael George 'Mike']

* An example of how confused the Confederate authorities were about the brothers' names.

More about Michael George 'Mike':
  GeoSource Information; Ancestry.com. Andersonville Prisoners of War [database on-line]. Provo, UT, USA: The Generations Network, Inc., 1999.
  Original data: Andersonville, Georgia.
Andersonville Prisoner of War Database. Andersonville, GA, USA: National Park Service, Andersonville National Historic Site.
Side: Union
Unit Name: 17 Iowa Infantry
Regiment: 17
State: Iowa
Function: Infantry
Company: B
Rank: Corporal
Type: Possible prisoner
Capture Date: 11/24/1863
Capture Site: Chattanooga, Tennessee**
Alternate Name: Kahler
Alternate Name: Kohler
Remarks: **POSSIBLE PRISONER**

**Site of the Battle of Missionary Ridge in which both brothers served, and where 'Mike' was taken prisoner, explaining his 'missing in action' notation, perhaps to be placed at first in the infamous Libby Prison with other Iowa POWs, captured at the Missionary Ridge RR tunnel; however, for the record, the action on 11/24 was on nearby Lookout Mountain: http://www.civilwarhome.com/lookoutmountain.htm

And this file note for George M.: Andersonville Prisoner of War Database.
Surname:     George Kahler
Company:     B
Regiment:     17
State:     IA
Arm of Service:     INF
Remarks:     (POSSIBLE PRISONER)
Page:     0
Code:     54626
GRAVE:     0
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Battles in which the 17TH REGIMENT IOWA VOLUNTEER INFANTRY took part (including Missionary Ridge):
Battle of Shiloh
Battle of Corinth
Battle of Port Gibson
Battle of Raymond
Battle of Champion's Hill
Battle of Big Black River
Siege of Vicksburg
Battle of Kennesaw Mountain
Battle of Atlanta
Battle of Jonesboro
March to the Sea