They are gray in color, which makes them a little tough to spot on certain terrain. They fire those red colored missiles with the red trails and when they explode they create a flame ball that lasts for a few moments. Stay clear of these explosions or better yet, hit the missiles with your lasers from a distance to avoid much damage to your shields and ship. AMTs are unshielded and will go down after only about four blasts from your lasers. Their firing rate is also pretty slow.
HAGs are really well armored despite having no shields and they fire a very powerful payload.
They won't target your ship because of their slow rate of fire but the installations that you are out to protect will take a huge beating. Think of them as the Trade Federations version of the howitzer. HAGs take multiple passes to take out, even using your secondary weapon. The trickiest thing about shooting down the slow moving bombers is that the thin shape of their fuselage makes them hard to hit with your lasers from behind or when they are coming at you. You never have to worry about getting fired upon by a bomber though, but the ground installations that you're trying to protect will get a beating if you're not quick at eliminating them.