This achievement is for destroying one of Leonardo's War Machines. The War Plans that you need to unlock this mission are located in the Centro District in Rome. You will enter an area and you have to search and find the Overseer (easily doable with Eagle Vision). Kill him, and collect the War Plans.
At this point, you can carry out the mission "Loose Cannon". After you complete the final objective, you will unlock this achievement. If you were like me and simply had trouble finding my way to the mission, this should be enough.
For a step-by-step guide, simply refer to Section 13 of the Assassin's Creed The Ezio Collection full walkthrough by Starlight126, xDaff, and Dang3R Gaming.