The book featured a human bureaucrat who was attempting to retrofit tachyon technology onto fighters in order to even the scales. Humanity was fighting with vat born humans and losing a war of attrition. The book featured some religious themes and touched on clones and hive humans. Not sure how accurate the physics was.
Possibly Exultant by Stephen Baxter, the middle book in a trilogy, which features a a war against the alien Xeelee. As the linked article states:
The mysterious Xeelee are far more advanced but less numerous than the humans, and the war has been at a stalemate for three millennia even though the entire Coalition has been directed toward the war effort and ten billion humans die at the front every year.
Commissary Nilis of the Office of Technological Archival and Control, part of the Commission for Historical Truth, defends both the older Pirius (whom he calls "Pirius Blue") and the younger one ("Pirius Red") but loses the trial. Pirius Blue is sent to a penal unit at the front as a foot soldier, and Pirius Red is remanded to the custody of Commissary Nilis, who has plans for the fruits of Pirius Blue's battlefield victory. Using the Xeelee fighter and the innovative tactics that saved Pirius Blue, he starts to plan an unheard of assault on the Xeelee's primary stronghold at Chandra itself.
While Nilis and his new team struggle to confront ossified government and military institutions, they try to understand and to develop new and sometimes alien technologies: FTL computers, a gravastar shield to protect them from FTL foreknowledge, and a black hole gun, capable of disrupting a supermassive black hole's event horizon.
Although the article doesn't mention it, this book also features scenes involving the human-hives associated with a religious group that were a major element in the earlier book Coalescent.