I received this book for free from the author, Robert Kroese, in exchange for a review.

I'm a sucker for the premise of this series: stranded spacemen teach Vikings to build spaceships. Rebuilding civilization from scratch is a venerable conceit in science fiction. This is usually fun, and it overlaps nicely with the method of good hard science fiction, which leaves the reader usefully instructed in certain principles of physics or biology after reading a story that otherwise closely resembles a Western.

The motives of the protagonists vary quite a bit. As do their specialties. Calvin Morrison was an ex-military State Trooper with an interest in history. In the interest of survival, and love, he sets himself up as a warlord. Martin Padway was an archaeologist, and lacking the technical skills common to men in his situation, he uses his excellent memory of pithy quotes and knowledge of distillation to become a kingmaker.

In this case, our protagonists are the doomed crew of the exploration vessel Andrea Luhman. They are doomed because humanity is in the process of slowly losing a war against the only other sentient species humans have encountered, the Cho-ta’an. In desperation, the Andrea Luhman is looking for a refugium against the militarily superior Cho-ta'an.

Human vessel. This is your last warning. We will fire on you.

Mallick managed a chuckle. “If you were going to fire, you’d have done it already, you motherfuckers.” He paused a moment. “Don’t send that.”
The Dream of the Iron Dragon, p 68

What they find is something else entirely, a McGuffin of lost technology that promises hope for the human race, if only they can somehow return it to what is left of human civilization. This is a bit of a problem, since they find themselves stuck in the 9th century AD in northern Europe.

O’Brien, the wiry, sandy-haired geologist, nodded. “We’re landing on Earth during the Middle Ages to build a forge to fabricate a spaceship part so we can carry an alien doomsday weapon across the galaxy to save humanity.” Chuckles went up from the group. Slater frowned. “Well, it sounds ridiculous when you say it like that.”
The Dream of the Iron Dragon, p 88

I admire the setup of this series. We get a collection of scientists and technologists with the crew of the Andrea Luhman, who are actually on a scientific mission when they stumble upon an artifact of great importance to the war effort. Thus, they really do possess the knowledge that will end up being useful in their quest. We also get a nice look at Viking society in the ninth century, which is a subject of interest.

This is mostly where the "usefully instructed" part comes in for me. As a fan of hard sci-fi, I like learning something new from the books I read. For this series, it is the life of the ninth century. For example, despite my interest in the Normans, frenchified Vikings, I hadn't heard of Rollo, Duke of Normandy.

I had heard of Harald Fairhair, but I didn't know much about his campaign to rule Norway. Not fun, at least for the people on the receiving end, is the answer. This isn't particularly surprising, but Kroese makes it real for me. This is an alternate history, but now I feel like I have a better sense of what our actual history was like.

The descendants of Rollo, and the other Vikings who raided France, would eventually go on to conquer England, as well as Sicily, and parts of the Levant. They still own a large fraction of the United Kingdom. All in all, we should probably consider them one of the most successful ethnic groups in all of history.

Of course, this is of little importance to the crew of the Andrea Luhman, who are preoccupied with matters of greater importance, like the survival of the human race, and their own. For them, finding a way to return their discovery to the remnants of human civilization in their own time is the only way to prevent extinction at the hands of the Cho-ta'an. The odds are long, but the payoff is enormous. They judge it a risk worth taking, which makes for a fun book for me. I look forward to their future adventures. ( )