The health and armor system in EDF 2025 can be a bit confusing compared to EDF: IA. Basically, you increase your health by increasing your armor rating. When taking damage, armor rating is pretty much meaningless and all damage applies directly to your health, unlike other games where armor is damaged first and health is only damaged after armor is depleted.
To increase your health you need to increase your armor rating, and to do that all you need to do is pick up the large red ARMOR crates that are dropped randomly by defeated enemies. My recommendation is to defeat all enemies on the map except for one or two weak enemies like ants, and then run around the map picking up all the red ARMOR crates (as well as the green WEAPON crates) before defeating the last enemy.
As far as how much each crate increases your armor rating, this varies by class. None of the classes get a 1-to-1 increase, unfortunately.
For Air Raiders, the ratio is 0.464-to-1. The key is to just pick up as many crates as possible during each mission. In addition, there is no practical limit to how high you can increase your armor rating, so you can grind it up as high as you want to.
When playing split screen, Armor pick-ups will apply to both characters. For example, if playing a Wing Diver and a Fencer, both will get credit for the armor pick-up. If playing two of the same class (i.e. two Wing Divers) you will get double credit for the Armor pickups. This is true for both Offline and Online missions. As a side note, if playing Offline, weapon pickups will only be credited to Player 1. If playing Online, weapon pick-ups will be credited to both players.
Thanks to Humpyrton for letting us know that if you are playing Online split-screen, weapon pickups will be assigned randomly to one of the two characters, but in Online MP mode both players get a weapon.NOTE: Thanks to
DominationQ for the information that if you are playing split screen with another class, and that class reaches enough health to unlock the achievement for that class, the achievement will not unlock until you complete a level playing as that class.
When your Air Raider's health (armor rating) reaches 1,000 then this achievement will unlock when you complete the level.