battlefield-3
There is a jet (and helicopter) upgrade called "Below Radar" that states:
When flying at low altitudes your heat signature is decreased, hiding you from enemy radar and preventing enemy air-to-air missile systems from locking on to you.
I can't find it anywhere in my loadout screen even though I've unlocked it, and it doesn't seem to be a passive perk that's always on, as I can always be locked onto by enemy aircraft.
Is this a bug or am I just missing something?
Any class and any weapon can lay down suppressive fire. The amount of suppression achieved depends on 3 things:
The proximity of the bullets to the person
The size of the bullets fired (bigger bullets, and especially frag rounds and explosives, will achieve more of a suppressive effect, so an smg will have less of a suppressive effect than a sniper rifle)
The amount of bullets fired (the suppression effect continues to stack until it reaches the cap, so an smg can be just as suppressive as a sniper rifle, but will require more bullets).
All of this coupled together makes the Support class generally the best class to purposely lay down suppressive fire, as using the bi-pod will make you accurate enough to get close proximity, your bullets are large enough to achieve quite a good suppression effect per bullet and you can fire much more than any other class to reach the suppression cap much more quickly.
With that said, generally, you won't purposely try to lay down suppressive fire much (unless you're in a really good squad who actually communicates and works as a team), you'll generally be taking a few shots at an enemy and a few will miss, causing suppression, and as long as they're at least a little bit suppressed, you'll get the suppression bonus if someone else kills them (they don't need to be very suppressed at all, just enough to cause the screen blur).
The bar represents your progress towards the next unlock in that weapon group. The more you use a certain weapon class, vehicle, etc, the more you points you will earn toward an additional unlock in that category. You can see a more detailed view of this progression in your battlelog profile:
Best Answer
It's altitude based, not terrain based. Just because you're skimming low over a mountain cliff doesn't necessarily mean you're under the radar barrier altitude. Keep the map's geography in mind. When you want to be below radar you must be near sea level.