Having worked for, and taught firearms for, 3 separate agencies, I can tell you that there is no uniform "one way" to carry it that every agency uses.
The largest was a federal agency ( now over 12k) carried "tube loaded, action locked, "on cock" (meaning the action bar lock had to be depressed to rack it), and on safe. This took 3 actions to accomplish before firing was possible. (action bar lock depressed, fore end racked, safety taken off).
Sometimes called "Assembly area load".
The second (also a federal agency of over 2100) carried it "off cock" (dry-fired on an empty chamber), off-safe, tube loaded. This required 1 action before firing was possible (fore end racked). Sometimes called "Gun box" or "gun bag" load.
The third, my first agency required "off-cock", tube loaded, safety on, requiring 2 actions before firing (fore end rack, safety taken off).
It all came down to whether the need was perceived to be immediate and the amount and frequency of training each officer or agent received, as viewed by the administrators. They all will work, but none had a round in the chamber, as noted in previous posts. I currently tell those that are on a multi-agency task force to check with the others, and be sure how each carries their shotgun - just as each family member should know, if neccessary, in the home.