The Wikipedia article on drill commands indicates that "arms" is not used today as part of any drill command in Australia, Canada, New Zealand, or the U.K. But it appears in several U.S. drill commands: "present arms," "order arms," "right shoulder arms," "left shoulder arms," and "port arms."
One noteworthy feature of the present-day English-language drill commands listed in the Wikipedia entry (both British Commonwealth and U.S.) is that none of them include "your"—whether with "arms" or with any other noun. For example, U.S. commands include "open [your] ranks, march," "close [your] ranks, march," and "stand at [your] ease," in addition to all of the "arms" commands noted above; and British Commonwealth commands include "change [your] step on the march," "stand at [your] ease," and "mark [your] time."
The instruction "present arms" seems to be of British army origin and goes back more than 200 years, as we see from John Russell, Instructions for the Drill, and the Method of Performing the Eighteen Manoeuvres, Third Edition (1804). Here is the entire eighteenth manoeuvre, called Advancing in Line, as Russell details it:
THE CHIEF.
THE BATTALION WILL ADVANCE—March.
It marches 100 paces.
THE CHIEF.
Halt.
FIRE A VOLLEY OBLIQUELY TO THE RIGHT.
MAKE—Ready——Present— Fire——Load.
FIRE A VOLLEY OBLIQUELY TO THE LEFT.
MAKE—Ready——Present— Fire——Load.
THE BATTALION WILL ADVANCE—March.
When the Battalion has advanced 100 paces,
Halt.
FIRE TWO VOLLEYS TO THE FRONT, AFTER THE LAST, THE MEN WILL PORT ARMS AND HALF COCK.
BATTALION Ready— Present— Fire——Load.
BATTALION Ready———Present— Fire, (the men will port arms and half cock.)
SHOULDER—Arms——SHUT—Pans.
REAR RANKS, TAKE OPEN ORDER—March.
THE CHIEF, and the Lieutenant Colonel, now dismount, and come through the center into the front, as do the music ; every one takes his station exactly as they had been placed when receiving the general.
THE CHIEF, with his back to the regiment, gives the words,
THE BATTALION WILL ADVANCE—March.
On the word March, the music plays, and when the battalion has advanced within 50 paces of the general, THE CHIEF gives the word Halt—GENERAL SALUTE—PRESENT—Arms, music plays God Save the King, and the drummers beat a march.
When the music ceases, THE CHIEF, turning to the battalion, gives the words, SHOULDER—Arms.
REAR RANKS, TAKE CLOSE ORDER—March.
Russell's book (on page 180) lists a number of "words of command," none of them modified with possessives. These include "ORDER—Arms," "FIX—Bayonets," "SHOULDER—Arms," "PRESENT—Arms," "HANDLE—Cartridge," "DRAW—Ramrods," RAM DOWN—Cartridge," and "RETURN—Ramrods." To this list, the eighteenth manoeuvre adds the memorable "SHUT—Pans." Evidently, the absence of "your" before "arms" is part of a much more broadly applicable style of wording commands.
I suspect that the "your" dropped out long ago because members of the battalion or squad already knew that all of the orders were directed to them in connection with their individual arms, ramrods, cartridges, feet, marching order, or ease; and to include the possessive would be a waste of breath for the chief, who (then as now) clearly needed to conserve it for more important purposes.