Is it possible to escape from a sunken U. S. submarine?

Yes, it is possible but only in limited circumstances. There were two escape trunks on the WW2 era boats, one in each torpedo room. The escape procedure was generally thought to have been workable down to 200 feet. Experienced divers could escape from as much as 300 feet down. However, most sailors had only had experience in the 100-foot escape towers in New London or Pearl Harbor. Even that was in controlled circumstances with Navy divers available in case of problems. In addition, during the war, not all submarine sailors went to Sub School where they would have gone through an escape tower.

Another limitation is that, inconveniently, most of the ocean is far deeper than 200 feet. Only 1 or 2% is less than 250 feet deep. The average depth of the Pacific Ocean is around 13,000 feet deep. The greatest depth is the Challenger Deep in the Mariana Trench at about 36,000 feet, or seven miles.