Glomar Explorer went a lot further down than that.
Yeah, but she failed and lost most of the sub - and was scrapped by Chinese breakers in 2015 anyway. This wouldn't be any classified sneaky operation where 'well we got a little bit' is okay because it's the cold war, either. Let them rest.
Fortunately, it's not so deep that you need top-tier submersibles to get there (compared to, say, Titanic or the Trench), so it shouldn't be too hard to get a good investigation down there and find out just what happened.