Keystone in German = Schlußstein
WW1 - OPERATION Schlußstein - German naval attempt to occupy St Petersburg. (Muh Russia) was aborted
Then on 28 Oct through 2 November, 1918 —
A German naval mutiny
Read about it here: https://en.m.wikipedia.org/wiki/SMS_Thüringen#Subsequent_operations
Dates are interdasting
Q often pointing us to watch the water, tell of submarines. Military planning.
Any possible answer for the KEYSTONE question?