Some 75% never came back.
The only military arm that suffered a casualty rate even close to that was the Allied bomber crews over Europe.
The U.S. Merchant Marine had the highest casualty rate of any American service during World War II, with approximately 1 in 26 mariners killed. This translates to around 9,300 deaths out of 243,000 mariners. The Merchant Marine played a vital role in supplying troops and materials, but their ships were vulnerable to enemy attacks, resulting in a high number of casualties.
It’s kind of hard to get out of a submarine when a hole gets poked in it while it’s under water.