Howitzers were used by the Union cavalry at the 2nd Battle of Collierville, Tenn on November 3, 1863.
Here is some excerpts from Edward Hatch's report of this engagement.
This describes how Hatch had the 7 Illinois Cavalry defend the stockade with 2 howitzers. After the Confederates committed themselves to a battle, the remaining forces of the 2nd Iowa Cavalry with a section of howitzers rode in and deployed for battle. It also mentions the 6 Illinois Cavalry had 4 howitzers but I don't think they arrived at the battle. The Confederates had some artillery but they left them in the rear so they could make a quick attack on the fort with only 2 brigades.
Collierville, Tenn November 9, 1863
On the morning of the 3d of November, Collierville was occupied by eight companies of the 7th Illinois Cavalry, and two iron howitzers, in command of Lieutenant-Colonel Trafton, with outpost 8 miles south on Coldwater.
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I was at Germantown with eight companies of the 6th Illinois Cavalry, four mountain howitzers of the 1st Illinois Light Artillery, 450 men of the 2nd Iowa Cavalry and a section of mountain howitzers, commanded by Lieutenant Reed, 2nd Iowa Cavalry.
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I immediately ordered Lieutenant-Colonel Trafton to throw the forces at Collierville(aka 7th Ill Cav) into the stockade, . . . and also ordered the 2nd Iowa (Cavalry) to move rapidly toward Collierville, to halt in timber 1 mile from town; to make no show of force until the enemy were in town, or they heard the howitzers in the fort, then to move rapidly forward and come into position north of the railroad, with the left of the 2nd Iowa resting on the stockade, the regiment dismounted.
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I immediately moved forward at a gallop, the 2nd Iowa going in at a run in columns of fours, moved quickly by the right flank to the railroad, and prepared to fight on foot, their howitzers in the center. ... Mounted and dismounted men of the enemy came forward in fine style, the howitzers of the 2nd Iowa cavalry firing rapidly.
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The 1st Illinois Light Artillery coming into position at a gallop on the ridge east of town under heavy fire, losing one-half of their horses killed and wounded, opened with canister, driving back the enemy's right.
. . . . . . (summary & recognition of troops)
The guns in the stockade were ably served by Lieutenant Wainwright, 7th Illionis Cavalry.
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Signed: Edward Hatch, Colonel, 2nd Iowa Cavalry, Comdg. Third Brigade