The Whatziss, revealed

Bad Cat Robot got it right first. Ball bearings. Those gunners were indeed cleaning and lubricating the ball bearings for the rotating platform of a large gun.  Many of the johnny-come-lately's further correctly refined things, but since they didn't play in earlier rounds, I have no idea if they were the beneficiaries of previous analysis, or just coming in late and seeing the whole thing in context...

Austro-Hungarian M14 42cm coastal howitzer being emplaced on the Italian Front during World War I. Coastal gun, but being used by the *koff* mobile army. World War I was really the last hurrah for this kind of thing (some examples during WWII, including the US "Little David" mortar notwithstanding) as the maturation of the airplane, and the logisitical costs of these things made them untenable. It took 32 rail cars to move this monster, and since it fired shells weighing 1000 lbs (kgs), it consumed an enormous amount of log tail to keep it shooting. When you can do the same thing cheaper with an airplane dropping a 1000 lb bomb...

BCR's prize?  Shooting party at the Castle, if she ever bestirs herself from the PNW and risks agoraphobia here in the Great Plains, where mountains don't hem your view...