This achievement is obtainable on Mission 7 where you must escort a convoy through the Zavian Abyss. For this achievement you cannot lose any of the three GR-75s you're escorting - this is also a medal for this mission, "Fully Escorted".
For the most part, you need to take out the bombers before they take out the convoy. There are two waves of this in the mission, and the convoys do not heal, so it's best to make sure you take out the first wave quite efficiently. Your team will tell you when the bombers are inbound, and you can just cycle through the targets with
to make sure you get them all, I'd ignore the TIE fighters / interceptors here. As previously mentioned, there's a further wave of bombers a little later on, while the tractor beam is charging. Obviously lowering the difficulty here can help if you're struggling.