Old Man's War is a series of Space Opera novels by author John Scalzi in the Old Man's War Universe. They follow the recruits of Earth's Colonial Defense Force (CDF), tasked with protecting Mankind's far-flung colony worlds from ruthless alien species. All recruits to the CDF are elderly citizens; the minimum sign up age is 75 years old. Recruits sign up while they are still on Earth, having already lived a long life, and are then given young, genetically-enhanced bodies upon joining the CDF.
In the early days of human colonization it became clear that human soldiers were not cut out for fighting the endless hordes of alien aggressors.The spirit was willing, but the flesh was found wanting. Humans were not strong enough, tough enough or fast enough to compete with the countless xeno breeds that desired the eradication of the human race. Humanity was saved by two technologies: the ability to grow an engineered human body to maturity in a few months and the ability to transfer a consciousness from an old body to the new one (provided that the brains are identical). This tech is the foundation of the Colonial Defense Force, allowing them to recruit senior citizens from Earth and transfer their minds to new super-soldier bodies. The most noticeable features of the engineered bodies include chlorophyll enhanced dermis for energy absorption, the above-mentioned brainpal, yellow eyes that appear like a cat's eyes for enhanced vision.
The Colonial Defense Forces use nanotechnology in almost every aspect of their military operations. Combat armor is made from interlinked nanobots, medical nanobots perform surgeries and help to regrow limbs, and the very blood of the CDF soldier has been replaced by a nanotech solution called "smartblood" that does everything that blood can do, only better (such as holding one's breath for over six minutes), and a few things that blood can't do (like explode on command). The primary infantry weapon, the MP-35 or "empee", assembles its ammunition on demand from a block of raw materials (with six types of ammo: rifle, shot, grenade, missile, flamethrower and microwave beam), and can use its ammunition block for self-repair.
The BrainPal is a neural implant that allows members of the Colonial Defense Forces (CDF) to send and receive data, including speech, battle plans and much more. CDF soldiers use their BrainPals to translate alien languages, watch classic cartoons, and read old books.
A BrainPal allows a CDF soldier to operate colonial technology by thought alone. A CDF rifle can only be used by someone with a BrainPal.
To the members of the Ghost Brigades the BrainPal does much much more: it provides a synthetic consciousness that allows the newborn soldiers to function until their own identities develop. This gives people who meet Special Forces the impression that they know everything. When presented with a situation that is unfamiliar to the newborn soldier, the BrainPal loads the relevant and important information directly into the mind at an amazing rate.
A form of FTL interstellar travel called a Skip Drive exist in the Old Man's Universe. The Skip Drive takes an object like a space ship, punches a hole in space, and places the object at its destination in a new, essentially identical universe. There are limits on the skip drive due to the characters not knowing all there is to know about how it works. The limitations are as follows:
The object skipping must not be near a major gravity well.
The object skipping cannot skip out too far.
The Colonial Union and other governments use devices called skip drones to communicate. These skip drones are essentially computers equipped with skip drives. A ship or satellite will launch one of these devices away from local gravity wells and skip to its target locale and upload its information to the local people.
More advanced races, notably the Consu, have a more complex understanding of skip drives and can even detect ships skipping into a system.
Old Man's War (2005, John Scalzi)
The Ghost Brigades (February 2006, John Scalzi)
The Last Colony (April 2007, John Scalzi)
Zoe's Tale (August 2008, John Scalzi)
The Human Division (January - April 2013, serialized ebooks; collected, May 2013, John Scalzi)
The End of All Things (June 2015, serialized ebooks; collected, August 2015, John Scalzi)
Aliens in the Old Man's Universe