Warrior's Scar. The Warrior Chronicles, #1

A reclusive military specialist from the early 21st century, Cortland Addison travels three hundred and four years into the future with Sköll, his rescued wolf. To the United States government, his journey was designed to test a strange technology. To Cort, it was a way to finally escape a society he no longer wanted to participate in. Cort and Sköll arrive in the future to find themselves barricaded in a vast underground cavern filled with everything they might need to survive their unknown future.
From how-to books to enough weaponry and powered armor to wage a war, Addison was well prepared to face whatever challenges awaited him. Or so he thought. For more than three centuries, the family he didn't know existed had been waiting and preparing for his arrival. In a world transformed by plagues and technology, Cort has become a legend within that family. Now it was up to the family legend to make good on the centuries-old promise, 'Hope lies in the blood.'