Or 17, which was what my brother did in '61. They dangled an E-8 to him if he'd re-up after 20 years, but he'd have to serve on a ship with a Captain he hated.
He said no thanks.
But if he hit 30 years he would get 75% of his base pay for life. Vice 50%. Quite a big carrot to give up. That captain must have been a pretty tough captain.