Philip K. Dick 
Mr. Spaceship [EPUB ebook] 

In Mr. Spaceship, humans in the distant future are at war with alien life forms known as Yuks. Using outdated, mechanical machines to wage war against the life-based weapons of the advanced Yuks, a research team decides to build a spaceship powered by a human brain. Enlisting a dying professor who agrees to donate his brain to the project, the humans believe they have turned the tables on the Yuks. But the spaceship has other plans.