In the early 80s I read a two-book science fiction series and I cannot remember the names of either book.
The first book was written in the first person and was about a war between a group of planets allied to Earth fighting against another group of humans called The Guardians who left Earth a century before and were building forces to come back and take over. The main character is part of a survey service that is about to be shut down and in a bid to keep going dispatches all of its fast frigate survey ships with under strength crews to explore new worlds. The main character are the only crew on the ship. Eventually they get sent on a new mission to take an experimental teleport device to a planet that has been invaded to allow troops to be sent. The main character sneaks onto the orbiting asteroid habitat and eventually gets to the planet and tricks the Guardians into helping him. Then in the last phase they must fight a massive carrier space craft which can enter the planet's atmosphere, becomeing a flying carrier. They win but still must find the Guardians.
The second book is written in the third person and continues the war. New characters include kidnapped space crews and passengers forced to use their technical skills working for the Guardians. We also meet a group of aliens living on another planet in the Guardian system who are expert biologists, they are all female until we eventually find that the small barely intelligent animals always near the settlements are the males which all the females are biologically compelled to mate with. We also learn that each female is destined to lose their intelligence and become a male, making a large part of their society nihilistic. They help the Guardians make biological weapons to destroy the Earth war ships. We also meet up with the main character's wife who is the fighter group commander on a British space fighter carrier and train character who has been arrested for talking out about the misconduct of the war. All three sides come together when the main character must lead a mission to save the Guardians from the nihilistic aliens out to destroy all life everywhere.
Overall, the technology in the story is relatively hard science with only a few things that aren’t. The ships spin for gravity, and accelerate and decelerate like modern rockets. The landers are rocket-shaped and take-off and land vertically.
Sone of the memorable scenes from the first book are when soldiers use bubble-like rescue spheres to re-enter the atmosphere and parachute onto the Guardian carrier, as well as the detailed, realistic space battle scenes.
A few details from the first book that stood out was that the main character named their ship after his wife and that she named the landers Stars and Stripes and Uncle Sam (I think) and painted them to match.
A few details from the second book was that the aliens were six-legged greenish centauroids and lived mainly nomadically. The main characters used a Vera ice shuttle to sneak past the guardian radar defenses. Also, the uncle of the main character's wife is a drunk about to be kicked out of the navy who ends up being the only flag officer to survive the Guardians' surprise attack on the fleet and becomes the leader who leads them to victory.