Polish Leopard 2A5's taking part in some driver training (and maintenance at end of video) The main armament is often placed over the back decks during driver training (in the Gun Clamp -Travel Lock I believe the Americans refer to it as) for several reasons but in the main it means the commander can fully concentrate on the "driver" and his intsruction and not be concerned about where the turret (and gun) are placed. Video from 2016 in Zagan,Poland | The Challenger

Poland’s Leopard 2A5 vs Russia’s T-72B3_ Cost Per | military defense