A spaceship crewed by a physically and psychologically scarred crew must fight off hostile aliens called the Jillies/Gillies and destroy their home world. Novel circa 1970's.
This could be Richard C. Meredith's We All Died at Breakaway Station (1969), as referenced in this previous unaccepted answer to a question about a novel with a similar premise. The enemy aliens are called the "Jillies", as seen in the quote from a review in that answer:
Now the Jillies are massing to attack Breakaway Station. This station is only lightly defended and unless reinforcements can be delivered in time, the Jillies will take it.
Earth however has no regular forces close enough to protect the station. The only possible reinforcement is a hospital ship and the two battle cruisers escorting it back to Earth. The hospital ship carries the frozen remains of thousands of solders who may still be revived and repaired. The crews of the ships are war casualties themselves, still desperately injured, temporarily repaired, some rebuilt as cyborgs.