From Halopedia, the Halo wiki
The Umbra is an arch-shaped ground vehicle that features the same anti-gravity technology most standard Covenant ground vehicles use. At the top of the Umbra's arch is the driver's cockpit and a gunner's seat with a plasma cannon. Below the driver and gunner seats is the carrier pod. On each side of the Umbra's carrier pod is a square, luminous touchpad that, when pressed, releases the lock and causes the outer wall to lower and extend a ramp leading into the vehicle. The ramp on each side of the vehicle leads to ten troop stations for a total of twenty troop stations per carrier pod.
Usage on Netherop
In 2526, Kelly-087 witnessed the Covenant deploy two Umbras via air drop by a Mokol'ta-pattern Spirit on Netherop. With some assistance, Kelly-087 was able to secure an Umbra  and rendezvous with Amalea Petrov and her First Platoon in order to aid John-117 and the rest of Blue Team on their mission to secure the Covenant frigate, Lucky Break.
List of appearances