Another one of the spin-off series of Girls und Panzer. Ribbon Warrior is about Shizuka Tsuruki and Rin Matsukaze entering into the sport Tankathlon which differs from what is seen in the parent series.
Here are the first 10 chapters in a batch that have been typeset to this point. If you have any interest or experience and wish to help with scanlations, be sure to visit the info link and take a look around.