[Ads-l] "H-Hour" and "J-Day", 21 Feb 1918

[dave@wilton.net]

The OED has 17 September 1918 for "H-Hour," but I've found this from 21 February:
 
Headquarters, 16th Infantry. “Plan for Raid on Richecourt Salient.” 21 February 1918. World War Records First Division A.E.F. Regular, vol. 10. First Division Museum. [ https://firstdivisionmuseum.nmtvault.com/jsp/PsImageViewer.jsp?doc_id=cdf20c52-01e6-47b0-ba0b-6574c9e5437f%2Fiwfd0000%2F20180808%2F00000002 ]( https://firstdivisionmuseum.nmtvault.com/jsp/PsImageViewer.jsp?doc_id=cdf20c52-01e6-47b0-ba0b-6574c9e5437f%2Fiwfd0000%2F20180808%2F00000002 )[  ]( https://firstdivisionmuseum.nmtvault.com/jsp/PsImageViewer.jsp?doc_id=cdf20c52-01e6-47b0-ba0b-6574c9e5437f%2Fiwfd0000%2F20180808%2F00000002 )
 
"Artillery: From J minus 5 day to J day—Cutting gaps in the enemy’s wire at points other than that of the real objective, namely, Salient LAHAYVILLE and Salient 2520.

"[…]
 
"Box Barrage—A box barrage of 45 minutes duration will be held at H hour as shown on the sketch. At H plus 25 the box barrage will close down to the enemy’s first four lines which will be heavily shelled till close of operation."
 
I have no idea what the "J" stands for. Any info or guesses are welcome.
 
I was unable to antedate the OED's 7 September use of "D-Day." I think that the term may have been introduced for this operation. (I found one relating to the same operation in a field order of a subordinate unit dated 10 September.)

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