What was the Wehrmacht? A group of obedient yeasayers? A murdering band of thugs? An army of millions of abused young men? This series in 5 parts provides differentiated and conclusive answers based on the latest historical and comprehensive investigative research, bringing many new facts to light – among them documents proving for the first time ever, what many among the officers actually thought. Blitzkrieg, the lightning war, in German incorporate modern weapons and vehicles as a method to help avoid the stalemate of trench warfare and linear warfare in future conflicts. The first practical implementations of these concepts coupled with modern technology were instituted by the Wehrmacht in the opening theatres of World War II. The strategy was particularly effective to Germany in the invasions of Western Europe and initial operations in the Soviet Union. These operations were dependent on surprise penetrations, general enemy unpreparedness and an inability to react swiftly enough to German offensive operations.

As tides rise and fall twice a day, vast amounts of water swirl around the earth. This is a huge energy source that's currently largely untapped. An estimated 3000 gigawatts are available to be harvested globally, enough to power a third of the earth's homes. Yet compared to wind and solar, the technology needed to harness tidal power is still in its infancy. The power of the ocean’s tides is the last great untapped energy source on Earth. From sub-sea kites to floating platforms, teams of engineers are racing to perfect the technology to harness the vast flows of water.

What if we could travel not just through space, but through time itself? If you could travel through time, would you change the past or the future? What if you found it couldn’t be changed? What price does the time traveller -- and the people they are closest to -- pay? This is a journey from H. G. Wells' The Time Machine through ideas like The Grandfather Paradox and The Butterfly Effect to the professional time traveller that is the ever popular Doctor Who. Steven Moffat, David Tennant, Karen Gillan, and Neil Gaiman offer a unique perspective on the Doctor. Edward James Olmos reveals the hidden meaning of the language he created for the vision of the future that is Blade Runner. Bob Gale and Christopher Lloyd take us behind the scenes of Back to the Future, while Ed Solomon describes the joy of solving a time travel conundrum for Bill & Ted’s Excellent Adventure. But what would be the physical and emotional cost to the time traveller? Audrey Niffenegger explains what inspired her novel The Time Traveller’s Wife. And what if someone from the future tried to travel back in time to warn us? Would we believe them? From the apocalyptic tones of 12 Monkeys to the drama of Quantum Leap and the comedy of Groundhog Day, time travel is a subject that has been irresistible to the creators of every type of science fiction.

We’re going back to the moon. Plans are being made, hardware is being designed, built, and tested to return humans to the moon and beyond in a new era of American space exploration. This episode explores how we did it in the past, and how and why we will do it again. The moon is critical to future explorations: it will be where we learn to build sustainable colonies on other worlds.

From the detection of gravitational waves generated in space over a billion years ago, to discoveries in genetics here on Earth, we've collected the most compelling science breakthroughs and advances of 2016. Thanks to magnificent, hard-working scientists and researchers around the world, science keeps marching ever forward. And this year saw some discoveries that are absolutely brimming with the promise of greater discoveries, breakthroughs and quality of life in the future.

Take a look back at many of the most fascinating science stories of 2017, a year full of stunning advancements in individual fields of study, from astronomy to biology, geology to history – when we piece these discoveries together we see the year in a new light.