This achievement can be unlocked on any map with access to vehicles (does NOT need to be a DLC map).
When a tank is available, use the left thumbstick to select land vehicle/tank
, then click the
once. Select the Assault Tank (St Chamond) with the
button and enter into battle.
People will often wait on tanks respawning. In my experience on the assault side of operations maps, the respawn time is 60-90 seconds from the death of the last land-based vehicle. Once you have spawned an Assault Tank, it will remain as your default tank for all future missions until you change it. This saves those key seconds to get ahead of someone else pinching the vehicle spawn.
When in battle be aware that the Assault Tank is not particularly well armoured. The driver's main gun is powerful with good range and manoeuvrability. The secondary front gunner position is also a decent weapon to use if someone else gets the tank before you.
25 kills is all you need (accumulative across all maps and game types) and is straight forward if you play sensibly. Never jump straight into a battle. The best tactic is to manoeuvre around objectives and 'snipe' into areas with enemy soldiers. 'Assist counts as a kill' will also count towards the 25.