As Warwick said, the Tank day is annual, kinda "closing the season" event. Plus there is an "opening the season" with another special days, dedicated to various branches of ground equipment - the Engineer day, the AAA day etc., each year different.
Plus there are other events not connected with the mil. tech. museum
EDIT: BTW many vehicles struggled yesterday in the mud, ecen the Pandurs were slipping and I feared for the Khalid - its transmission is in bad shape and most of the time it struggled on lowest gear and made a terrible noise