The Lucky 13th Series by Rick Shelley

World War II had the Dirty Dozen. The war in space has The Lucky 13th. The 13th Spaceborne is the elite fighting force of the Accord of Free Worlds. Their do-or-die mission is to stop two enemy empires from poaching free worlds. As usual, they're on their own...

The soldiers of the elite 13th Spaceborne fighting force must locate a secret lab and liberate the scientists held there, before they become prisoners-or casualties-themselves...

The national bestselling author of the Spec Ops Squad series ends the saga of "The Lucky 13th,.". In book three of Shelley's science fiction-military trilogy, the soldiers of The Lucky 13th are spearheading the assault of the Accord planets. Heavy casualties are expected. But the fighters of the 13th know the odds-and how to beat them...