Short story about a man trying to seize control of a brainship
That's Solar Plexus by James Blish.
A man has had his brain removed and put in control of a spacecraft.
"Here," the voice said patiently. "I am the Astrid. I am also Murray Bennett. Bennett is dead, so he can't very well come into the cabin and shake your hand. I am now Murray Bennett; I remember you very well, Brant. I need your help, so I sought you out. I'm not as much Murray Bennett as I'd like to be."
Brant sat down in the empty pilot's seat.
"You're a computer," he said shakily. "Isn't that so?"
"It is and it isn't. No computer can duplicate the performance of a human brain. I tried to introduce real human neural mechanisms into computers, specifically to fly ships, and was outlawed for my trouble. I don't think I was treated fairly. It took enormous surgical skill to make the hundreds and hundreds of nerve-to-circuit connections that were needed—and before I was half through, the UN decided that what I was doing was human vivisection. They outlawed me, and the Foundation said I'd have to destroy myself; what could I do after that?
"I did destroy myself. I transferred most of my own nervous system into the computers of the Astrid, working at the end through drugged assistants under telepathic control, and finally relying upon the computers to seal the last connections. No such surgery ever existed before. Now I'm the Astrid—and still Murray Bennett too, though Bennett is dead."
Another man, the protagonist, is trying to take control of the ship, obviously against the wishes of the brain. He is prevented from entering the bridge by various defensive measures such as something like a scaled-up electric bugzapper.
Brant walked a little faster. How would Bennett's vicious brain child enforce his orders?
"I said, go back to your cabin," the voice said. Its tone was now loud and harsh, and without a trace of feeling; for the first time, Brant was able to tell that it came from a voder, rather than from a tape-vocabulary of Bennett's own voice. Brant gritted his teeth and marched forward.
"I don't want to have to spoil you," the voice said. "For the last time--"
An instant later Brant received a powerful blow in the small of his back. It felled him like a tree, and sent him skimming along the corridor deck like a flat stone. A bare fraction of a second later there was a hiss and a flash, and the air was abruptly hot and choking with the sharp odor of ozone.
"Close," Powell's voice said calmly. "Some of these rivet-heads in the walls evidently are high-tension electrodes. Lucky I saw the nimbus collecting on that one. Crawl, and make it snappy."
He eventually manages to seize control by throwing a boot across the bridge where it strikes a control panel and shorts it out.
"Ah," said Brant. Still sliding, he drew off one of his heavy shoes and hefted it critically. It would do. With a sudden convulsion of motion he hurled it.
Fat, crackling sparks criss-crossed the room; the noise was ear-splitting. While Bennett could have had no idea what Brant was doing, he evidently had sensed the sudden stir of movement and had triggered the high-tension current out of general caution. But he was too late. The flying shoe plowed heel-foremost into the autopilot with a rending smash.
There was an unfocused blaze of sound from the voder—more like the noise of a siren than like a human cry. The Astrid rolled wildly, once. Then there was silence.
I read the story in the mid-to-late 1970s, probably in an SF collection or anthology,
That could have been the 1975 anthology Human-Machines: An Anthology of Stories About Cyborgs edited by Scortia and Zebrowski.
and suspect the story was probably from the 1950s or 1960s.
In fact it was first published in Astonishing Stories, September 1941.
By the way, the 1952 reprint of this story contains the earliest known citation for the term gas giant.