This was originally meant to conclude Romero's Living Dead trilogy until he started the machine up again with Land of the Dead. Unlike racial politics of the first and the consumerism of the second, the third film in his series was all about the military industrial complex.
A small group of survivors are using a military base to scout for others. They land via helicopter, search and escape before the zombie hordes overtake them. At the underground base, scientists work with a captured zombie named Bub in an attempt to cure the zombie plague. The scientists believe brains will solve their problems and the military guys believe brawn is the way to go. There are endless caverns beneath the base where captured zombies are stored but others seem to be joining from parts unknown.
This is definitely the 80s installment of Romero's series in that everything seems pitched over the top. The movie doesn't make either side look particularly healthy. The lead scientist is conducting gruesome experiments. The military guys have only a one-track mind. Our heroes, such as they are, are fairly sensible but can think only of escape. The whole thing ends in a deadly tanglebang with very few people getting what they want. The most interesting arc of the movie is Bub, who learns how to use a gun and expresses basic emotions. The zombies becoming intelligent would get picked up on in the next movie.
I remember this one having pretty gory effects. Tom Savini, who did the effects for Dawn of the Dead, worked on this one and they are pretty brutal. Not for the faint of stomach.