Thirteen button trousers ...
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When I served, the blues had 13 buttons. The later uniforms had zippers and were really baggy; actually looking like they had been slept in for several days. ...I think the zippered trousers were put in to accommodate the more obese following generations of sailors. They looked horrible.
After that they went back to 13 buttons. But not practical for the pregnant ones who should not be there to begin with.