All that needs to be done is call in 3 ordnance drops in one game, not as easy as it sounds, but I know how it works, first off you can only earn ordnance in infinity slayer or the new majestic free for all mode no other game type and they need to be in the majestic dlc. By default an ordnance drop requires 70 points and after each one is called in the next one increases by 30%, you can make this easier on your self by equipping the ordnance priority which gives you 40% bonus to all points earned, although some work is still required as you do need alot of points, hope this helps break it down for you. If you give this a negative leave a comment so I know what I did wrong.
Also thanks to DragonFangDan for pointing out the team action sack gametype where you start the game with an ordnance already making this achievement much easier.