Take on daily Missions to earn Piggy Banks containing Coins, and, if you're lucky, Gems!
There are up to four Mission slots available, all with different sized rewards! The first three slots are unlocked as you level up your HQ, while the fourth slot becomes available when you activate the Beach Pass.
You can track your mission progress on the main screen by clicking on the submarine, and on the troop selection screen during battles.
Whenever you complete a Mission, just go back to the sub to collect your Piggy Bank rewards!