Comes from the ALLIED NAVAL CONTROL OF SHIPPING MANUAL (ATP-2) Options. The manual contains a large number of shortcut messages to relay information quickly.
BZ was one such shortcut which indicated a ship had done something well and only came from unit commanders (fleet/task force/squadron, etc) to a specific ship or from one CO to another.
Minor correction remove the “Options”. I think it’s volume 2B, but my memory is fuzzy after 20+ years.
SLIDE
Thank you. But do you know why those 2 particular letters were selected?