The phrase "as a second command" is correct and usable in written English.
It can be used when referring to an additional directive or instruction that follows a primary command.
Example: "The system will execute the first command, and as a second command, it will initiate the backup process."
Alternatives: "as an additional command" or "as a subsequent command".
While acting as a second command ship, 9 officers and 44 enlisted men were added to the standard crew.
While serving as a second command flagship or a flotilla leader, they had an additional three officers and fourteen enlisted men for the commander's staff.
While serving as a squadron flagship the crew was augmented by 13 officers and 62 men, and as a second command ship by 9 officers and 44 sailors.
The ships' standard crew was 31 officers and 446 enlisted men, with an additional 9 officers and 41 enlisted while serving as a second command flagship.
When one of them was a squadron flagship, the crew was augmented by 13 officers and 66 enlisted men; while serving as a second command ship, 2 officers and 23 enlisted men were added to her standard crew.
While serving as the second command flagship, the ship carried an additional 3 officers and 25 men to the standard complement.
She was assigned to the I Squadron as the second command flagship for the annual autumn maneuvers.
For the duration of her career as the second command flagship of the Cruiser Division, the standard crew was augmented by an additional nine officers and 44 enlisted men.
Gneisenau, when serving as the squadron second command flagship, had an extra staff of 3 officers and 25 men.
She had accumulated a total of 1,751 hours of flight time, of which 251 hours were with Sunjet Aviation as a second-in-command and 99 as a Learjet second-in-command.
It's a dauntless performance by Hinds (and some compensation for his oddly curtailed role as a second-in-command to Daniel Day-Lewis in "There Will Be Blood"), and it peaks with a formidable scene in a hotel bar, both a pastiche and a deepening of nineteen-forties noir, where Bill is propositioned by a low-lidded vamp (Charlotte Rampling) whose regard for humanity is even baser than his.
