G,
I must disagree with you about Jutland being the root event for the design of cage masts. I believe US battleships were converted from "military" pole masts to cage masts when they returned from the Great White Fleet cruise.
In Navsource, for the USS South Carolina, there is a copy of a newspaper article, dated 1909, showing "the new dreadnaught with her *** masts."
The Royal Navy went from military masts to tripods to provide a high, stable platform for spotting, and I believe it was even earlier than 1909.
Rick
*edit: apparently in 1909 they could write words on the front page of the paper that have come to be taken wronly nowadays.