The Forlorn Hope — David Drake

MARCH CROSS-COUNTRY
They had fought long and hard, and damn near won in spite of everything. But now the men who hired them are going to sell them to the enemy...and so begins a novel of adventure in which a band of Star Mercenaries is driven across the face of a planet by enemies bent on their destruction. With only the guns in their hands, this tiny band, this "forlorn hope" must battle star ships, artillery, treachery -- and the most powerful tanks in the universe. As they struggle from combat to flaming combat they come ever nearer to triumph -- and a final bloody test.