Here are two action-packed novels from David Drake's "Hammer's Slammers" series, which set the standard for military science fiction.
In Counting the Cost, the hottest science-fiction mercenaries are back, so why count the cost? The other guy is going to pay for it! Hammer's Slammers must win a two-front war while maintaining the civilian power structure against hordes of religious fanatics.
In The Warrior, Colonel Alois Hammer, Luke Broglie, Tess Kuykendall, and Slick Des Grieux - cogs in a killing machine - find themselves at the center of a potential bloodbath.