Two things: First, Tom Clancy was not a submarine commander. In fact, he never served on active duty in the military. He was an insurance agent in Maryland at the time his first book, "Hunt for Red October" was published.
Second, this would be a very difficult question to answer definitively for several reasons:
The size and breadth of Clancy's catalog is impressive and covers several areas. An expert on submarines, for example, might not have the same level of knowledge about armored warfare. Clancy has dozens of fiction and nonfiction books out and to have complete knowledge of his works would be a steep task, and one that an expert probably wouldn't undertake.
Information is classified and declassified all the time, and we can't even be sure that something he revealed in the 1980s might still not be classified. We can use submarines as an example. The US Navy has been (and is still releasing) thousands of pages of documents about the sinking of the USS Thresher, which sank in 1963. The accident occurred almost 60 years ago, and all of Thresher's sister boats have been retired since the mid-1990s, and there was persistent pressure to release these documents for remaining family members, yet much of it has still been unknown.
Part of Clancy's vast catalog includes dozens of works that included co-authors or ghostwriters. There's no sure way to delineate what he wrote, how much he contributed, or whether he simply lent his name to the cover to help sell books. At the very least, it seems possible that close to the end of his life, "Tom Clancy" was less an author and more of an intellectual property.
For all these reasons, it might be helpful if you asked a narrower question.
However, I don't want you to feel as though I've just shut you down. And there is probably some merit in your question. This short 1987 New York Times article describes an exchange between Clancy and the Secretary of the Navy:
Mr. Lehman, in an interview last week, recalled telling Mr. Clancy in a good-natured way: ''If you were a naval officer, I would have you court-martialed because of all the classified information in your book.'' Up to that time, Mr. Lehman said, ''operational procedures of antisubmarine warfare had been classified.'' But, he added, Mr. Clancy had simply ''pieced it all together by voraciously reading the open literature for 15 years, things like the Proceedings of the United States Naval Institute.''
The article is worth reading for some minor details about how Clancy got the information for his book. It's behind a paywall, but this account from the US Naval Institute (which published "Hunt for Red October") also says that Clancy spoke often with submariners that he met through his insurance business. This doesn't mean that Clancy was violating national security protocols, however. Any good intelligence operation, like the Soviet Union's, would also have spent time poring over "open source" materials like the USNI Proceedings and academic publications. If Clancy could get his hands on it and piece it together, then others could too.
After he became established, Clancy seems to have been vetted by the government for access to some classified information. Some of his non-fiction works, such as "Submarine" clearly required access and cooperation from the military, and surely would have been subject to prepublication review to prevent the release of classified information. Clancy clearly had a chummy relationship with the US government and the military throughout his career and that never seems to have been in danger.
Beyond that, there was certainly some speculative information in some of Clancy's works that seemed to hint at classified technology that was later revealed. For example, Chapter 17 of "Red Storm Rising," a novel about a NATO-Warsaw Pact conventional war, is titled "The Frisbees of Dreamland." It details a mission flown by the fictional F-19A. Here's a short snippet:
Lockheed called her the Ghostrider. The pilots called her the Frisbee, the F-19A, the secretly developed Stealth attack fighter. She had no corners, no box shapes to allow radar signals to bounce cleanly off her. Her high-bypass turbofans were designed to emit a blurry infrared signature at most. From above, her wings appeared to mimic the shape of a cathedral bell. From in front, they curved oddly toward the ground, earning her the affectionate nickname of Frisbee. Though she was a masterpiece of electronic technology inside, she usually didn't use her active systems. Radars and radios made electronic noise that an enemy might detect, and the whole idea of the Frisbee was that she didn't seem to exist at all.
The "Frisbee" is not an F-117, but it sure quacks like a duck. The F-117 was produced by Lockheed and was operational at the time the book was published but wasn't publicly revealed for a few more years. But in the case of speculative information in a work of fiction, it's also fair to wonder whether Clancy had real inside information, or just a general awareness of technologies and tactics that might be useful. The idea of a stealth aircraft to defeat radar and attack air defenses, like the Frisbee does in the book, wasn't a brand new concept at the time. It just wasn't publicly known that the US had an aircraft that could do it. You might think it an odd coincidence that he had correctly pegged Lockheed as the designer and manufacturer, but a reasonably informed person could have known that Lockheed had a reputation for producing top secret aircraft at the time. There are plenty of other examples like this throughout some of Clancy's books, but an exhaustive list probably isn't feasible.
Hope that answers your question!