Brumaks are large monsters aligned with the Locust Horde.
Capable of reaching sizes of 12 meters in height and 10000 Kilograms in weight, these behemoths are utilized as soldiers, mounted with large cannons. And as transportation, being used to carry Locust Drones into battle.
They are armed with guns on their wrists, as well as a large cannon on their back.
A Brumak appears at the end of Act 4, during the escape from East Barricade Academy. There is no combat with a Brumak in the Xbox 360 version of the game, but the PC version features a boss fight with a Brumak.
In a video of Gears of War 2, A Brumak can be seen getting its head blown off, and it is likely we will see more of these creatures in the game.