For the AI construct, see Black-Box.
In Halo Wars, Black Boxes are collectibles in the campaign that when collected, add new events in the Halo Wars Timeline. They look like black boxes with yellow stripes on them, and can be picked up by any unit. When the player collects one, they can just resign straight away and will still have it. Aerial units are the easiest and most direct way to collect them.
In aviation, the term "black box" refers to both flight recorders on commercial and other aircraft. The flight data recorder is responsible for recording flight parameters and the cockpit voice recorder is responsible for recording all communications in the cockpit of an aircraft in flight. The phrase has become popularized by modern media reporting on aircraft crashes.
Mission 1: Alpha Base
Head back to the last bridge you crossed before reaching Alpha Base's gate and peek underneath. The crate is below the arch, next to an overturned Warthog. You can drive down the small ramp to the left to reach it.
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Mission 2: Relic Approach
This black box is located northwest of the second base. There is an area blocked off by an energy shield. Destroy the power source with some infantry, and both the crate and a good chunk of supplies are yours for the taking.
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Mission 3: Relic Interior
This black box is located right from the beginning of the mission. Simply turn your Grizzly tanks around and head in the opposite direction of the objective arrow. You'll discover a separate pathway, winding to the northwest. At the very end, near a crashed Pelican, is the crate, with an Elite and a Jackal squad.
Mission 4: Arcadia City
Scroll to the western most base. Directly north of it is a column supporting a skyway. At the base of this column, on top of a few stairs, is the crate you seek.
Mission 5: Arcadia Outskirts
In the middle of the map, almost halfway between your original base and the northern Covenant base, there is an abandoned reactor that you can take over for an extra tech level. The crate is on the grass immediately to the west of this platform, near some ferns and an infantry cover spot.
Mission 6: Dome of Light
Wait until you place the third Rhino across the broken bridge using the "transport" power. Before leaving the area to concentrate on other tasks, check the western shadows for a short separate path. The crate is there.
Mission 7: Scarab
At the very top of the map, and as far east from the Scarab as possible, is a small area surrounded by cliffs. Look for the bountiful gathering of shiny blue supplies and you'll find the crate among them.
Mission 8: Anders' Signal
Directly southeast of the base, on a tree-ringed plateau, is the crate.
Mission 9: The Flood
On the western side of the map, near one of the Flood structures you have to put down. Nothing else really distinguishes this location, so check the minimap in the screen below.
Mission 10: Shield World
Team Bravo is blocking the path to the black box. Rescue them, and any unit can collect it or fly a Hornet over, drop down for the crate.
Mission 11: Cleansing
A Hornet is also required to get the mission's black box. It is resting on the northwestern flank of the ship, at the opposite end you found the skull. Note that by "flank," it means the very edges of the Spirit of Fire; beyond the fences, where the ship slopes downward.
Mission 12: Repairs
Like the last crate, this is on the outer edge of the ship (northern flank, southern tip), but tucked closer to the outer fences. Again, you'll need an air unit.
Mission 13: Beachhead
Head to the north-east edge of the map. Go to the middle of that edge. On a very high and flower-covered cliff is the crate. You can reach this via a ground unit, but as usual, an air unit is a lot easier and quicker.
Mission 14: Reactor
This crate is hidden southwest of the first Covenant base and the possible location of your second UNSC base. It's in a raised grass rectangle, bordered by metal, and you'll need an air unit to get there.
Mission 15: Escape
Compared to the skull, this is very easy. Just take a Warthog from your original base, drive north across the blue ring structure and you'll see the crate in a very obvious location.