How do you unlock weapon attachments?

[ZachBoardyHD]

i'm currently playing on the easiest diffiuclty and on mission 11 before moving onto the supersolider difficulty but I still have not unlocked most the weapon attachments from the weapons iv'e use, how do you unlock these?

 

Up to now Iv'e found this game a bit difficult to get through even playing on the easiest difficulty. Delta difficulty (The hardest difficulty) with Crysis 1 was a ton lot easier then this game despite the rairity difference on here

[MikeMan54]

Pick them up from dead soldiers or find them in the world, usually the visor gives hints. 

 

Then press and hold the touch pad to equip unlocked ones