Upgrade your base in the most efficient order

Metal Slug Defense offers nine different base upgrades on which players can spend their MSP (regular currency). Each of those upgrades can in turn be upgraded up to a maximum level of 20 (at present). Keep playing long enough and you'll eventually max them all out. But when you're just starting, upgrade order can influence the speed and difficulty of your progress through the game. So let's work smarter, not harder.

Your immediate goal should be increasing how much MSP you earn from completing missions so that you can better finance future upgrades. Start by upgrading MSP Gain. Level completion time plays a part in MSP payout as well. To beat levels faster and more easily, upgrade Development Speed, Production Speed, and Destruction Bonus (in that order).

Sortie Level (energy production) affects how much you can play, so work on it next. Much less important are Metal Slug Attack, Charge Speed, Hangar Level, and Base Level. Save those for last (and definitely prioritize upgrading units over Hangar and Base).