Is an ex-spouse automatically entitled to a percentage of your retirement pay in the event of a divorce?

No. The spouse must request in writing to the Office of Personnel Management. Get all the requirements on the same office. It shall be preceded by a court order.

How many years do you have? I had a good friend, E7 with four kids. He was deployed, and his bank account was empty, and his wife was gone when he returned. She's found a new man. They had been married for 15 years. The judge ruled that since it was over 10, she would receive 50%. He had about 17 years in at that point. He decided to ETS instead of retire. She was furious, but since there is no retirement fund, it is instead Retired Ready Reserve, there was nothing she could do.
Fast forward 4 years. He enlisted in a NG unit in California. His kids were either with him, or in college. He went into the Active Guard, then retired. She took him back to court, but the judge ruled he was receiving a state retirement, and not a federal military retirement, which was in the divorce decree.

Remember when they used to say that your wife and kids do not come in your "Sea Bag?" Well in Virginia they do, my ex got almost 1/2 of my retirement even though she is a pharmacist. I do not get squat from her, but she gets $650 from me a month. I think equal rights for women is a bunch of BS. It would be one thing if she supported me while I was in the Navy, but she was just a leech, a sucker, somebody who was just along for the ride. My only consultation is that she doesn't get all the other benefits (medical, dental, exchange, base privileges). Looks like the state I live in believes my ex is so incapable of taking care of herself that she deserve part of my retirement. Thank God I am rid of her.

In my case not automatically, it had to be part of the decree

If you were married for 10 years or more, the ex-spouse can get half your retirement pay. The state may have something to say about it also.

Anything that is yours cannot be given to anyone else without the over-reaching influence of a government agency.

Any person who takes any portion of someones retirement is a worthless piece of shit, regardless of the time served and years married. My ex-wife tried. That bitch wasn't getting a dime...other than child support which I have no problem paying.

I can tell you what they told me when I filed for divorce at nine years 11 months. Period. After 10 FAS but if you file before you reach 10 FAS dad should leave u alone but I'm not a lawyer.

Each Sate has rules. More often than not if you are married for 10 or more years they are going to get half.

Depending on how long they were married will determine the percentage of pay.