I saw this in a book. A person is told by his boss "You have to hit the decks running". This man doesn't know what his boss meant. Is this something about the idiom "hit the deck"? Does it mean "get to action quickly". Or, since this person doesn't understand his boss either, could it be some kind of misuse?
I think it's a old naval term - called into battle gunners would slide down companionways and hit the desks running to their position.
As has been said it means start doing productive work as soon as you start the job
Similar to "hit the ground running". Perhaps the person in your book substituted ground with deck because he's in a maritime setting. When you jump off a moving train or the like you have to "hit the ground running" in the same direction or you would fall.
Hit the deck running appears to be a blended idiom conflating the much older hit the ground running and hit the deck. William Safire, in his "On Language" column of 1 Nov. 1981, offers anecdotal evidence that it was indeed Navy jargon.
The expression doesn't appear to have entered common language much earlier than mid-twentieth century:
“We started last Spring,” says McDonnell, “and hit the deck running.” The result was that when technical appraisers from NASA's Langley Research Center and the Air Force came to award the first contract for Project Mercury—placing the first man in space—it went to the comparatively small (20,000 employees, among them 5,000 engineers) McDonnell company instead of one of the industrial giants among those 12 companies which bid. — Missiles and Rockets 5, 18, 1959.
James McDonnell did not serve in the military, but as an aircraft manufacturer he certainly came into contact with high-ranking members of all branches of the Armed Forces.
A query of Google Books yields a few more hits from the 60s and 70s, increasing thereafter. The lyrics to the song @TomBell mentions is an original composition from 1960 and use the term in a quite literal sense.
COHA only offers a stage direction from the 2005 film script of The Island:
Starkweather hits the deck running, sprinting up the avenue.
The earliest hit in COCA is an article in the Christian Science Monitor of 9 April 1990:
Chancellor Joseph Fernandez, who hit the deck running three months ago when he took on his new job, has just showed a reporter his proposed catch-up budget for school repairs.
And a search of the digitalized newspaper collection of the Library of Congress, which stops at 1963, only yielded articles with baseball scores (deck, run, hit).
A Google NGram shows the expression still to be relatively rare:
Given the paucity of these results, it's no surprise that someone might be confused by the expression, but it's similarity to the far more common hit the ground running should have been a strong clue.