Does anybody know where and when the KV "Big Turret" was used?

I think in the Eastern Front...
You can check this site:
http://www.battlefield.ru/

You'll definitely find something!

One here apparently photographed in Lithuania at the start of the Great Patriotic War. AFAIK only three of the unknown number produced (up to 20) ever got photographed.

KV-2

I took a look through it, under tank development/heavy tanks/KV-2

"Up north, the 6-Panzer-Division under Panzer-Gruppe 4 had encountered Russian heavy tanks. As related in the war diary of Panzer-Regiment 11 on 25 June 1941:

During the morning, the II.Abteilung/Panzer-Regiment 11 together with Kampfgruppe von Seckendorff advanced along the right-hand march route. Throughout the day both units fought off repeated attacks from the Russian 2nd Armored Division. Unfortunately, the Russian 52 ton heavy tanks showed that it was almost insensitive to hits from the 10.5-cm. Several hits from a 15-cm gun were ineffective and bounced off. However, continuous attacks by several Pz Kpfw lV managed to knock out a large number of tanks throughout the day, which allowed our own attack to again drive forward to about three kilometers west of Dubysa."
Tank from same battle:
"The KV-2 Tank from the 2nd Tank Division delayed elements of the 6th Panzer Division near the Rossienie town. Tank was immobilized by the German's 105 mm Howitzer but the crew continued fighting until run out of ammo."

Used to defend the Krupp's Essen plant against advancing U.S. troops.

Hi they wre only used very early on in the eastern front and to the best of information available only 6 were produced , the clue is in the placement and numbers of the turret climbing rungs on the side of the turret . cheers ian