Army of Two (EU)

Set your partner to aggressive, and every now and again he will fall down and call for healing. Just heal him 25 times, it doesn't matter if you drag him or not, it is more of a suggestion seeing as his initial spot will likely be under enemy fire.

It can be done by shooting your partner yourself, but this can be a tremendous waste of ammunition.

It is probably easier to find some good cover on the highest level of difficulty, and set your partner to aggressive on your position. That way he will pop his head out to be shot, but stay near you.

If your cover serves well, he will be downed at cover, and healing him will be simple and without delay.

Alternatively, you could always have a co-op partner run out and get downed on an easier setting, so that you can heal him, rinse and repeat.

Take a shotgun (DAO-X for example), start a China Mission (there is no enemy at the beginning). Then shoot your partner in head. He will knock down, when he's back on his feet, repeat. After few seconds he will need healing. Just hold 'A', you don't have to drag him anywhere. When he's ok - shoot him again. When you won't have any ammo left - restart checkpoint.

After 10-15 minutes achievement is yours.

not sure if you actually have to drag then heal but all you have to do is shoot your partner or let him die and heal repeat 25 times done

On the middle difficulty, you will probably get this by playing through normally by the time you hit Miami.