It is located very near to the famous Schwaben Redoubt, which the Division attacked on July 1, 1916. The Schwaben Redoubt was a little to the north-east of where the tower stands, and was a triangle of trenches with a frontage of 300 yards, a fearsome strongpoint with commanding views. It is also located close to the Thiepval Memorial to the Missing of the Somme.
The front lines were at the edge of Thiepval Wood which lies to the south-west of the road between the Thiepval Memorial and the Ulster Tower. Troops of the 109th Brigade crossed about 400 yards of no man's land, and kept on going. They entered the Schwaben Redoubt, and advanced on towards Stuff Redoubt, gaining in all around a mile, though not without losses. To their left, the 108th Brigade were successful in advancing near Thiepval, but less so nearer the River Ancre.
The 107th Brigade supported them, but although men of the 36th Division held out for the day the Germans mounted counterattacks, and as their stocks of bombs and ammunition dwindled, many fell back with small parties remaining in the German front lines. The casualties suffered by the 36th Division on the 1st of July totalled over 5,000.

The tower (plus a small cafe nearby) is staffed by members of the Somme Association, which is based in Belfast.

Other memorials in the grounds
At the entrance to the tower is a plaque commemorating the names of the nine men of the Division who won the Victoria Cross during the Somme. There is also a memorial here commemorating the part played by members of the Orange Order during the battle. The inscription on this memorial reads:
"This Memorial is Dedicated to the Men and Women of the Orange Institution Worldwide, who at the call of King and country, left all that was dear to them, endured hardness, faced danger, and finally passed out of the sight of man by the path of duty and self sacrifice, giving up their own lives that others might live in Freedom. Let those who come after see to it that their names be not forgotten."
http://en.wikipedia.org/wiki/Ulster_Tower_Thiepval