Swords and Saddles by Jack Campbell

The New York Times–bestselling author of the Lost Fleet series tells tales of an alien ambush, time-traveling cavalrymen, and a military lawyer in space.
In his New York Times bestselling Lost Fleet series, author Jack Campbell has taken readers and Captain "Black Jack" Geary on a fast-paced journey of conquest across vast reaches of space. Now, in the three novellas contained in Swords and Saddles, first in a series of short fiction collections from Jack Campbell, readers can explore the entire universe of Campbell's fiction. A new author's note accompanies each story.
Begin by entering "The Rift." Answering a distress call from a colonized planet, a combat team finds themselves ambushed. They manage to scrabble their way to a remote research facility in the countryside, joining a group of schoolchildren that have holed up with the researchers—three groups united in fear that their lives will last only as long as they can avoid...