Sunken SSN-593 - USS Thesher Connection
The Universal Ship Cancellation Society , a non-profit, tax exempt corporation founded in 1932, promotes the study and history of ships, their postal markings and documentation of events involving the U.S. Navy and other maritime organizations of the world.
The society sponsors convention exhibits and publishes a monthly "Log" that often includes informative updates on current subs and fascinating articles on naval history that might be very difficult to find elsewhere.
I just checked out the online Cover of the Month for March, which is actually a succession of three covers relating to USS Thresher SS(N)-593. Their story is revealed below the images. It is fairly short and you may want to read it for yourself. I will only add that "CAPT. Robert Rawlins, USN" has been a distinguished contributor to the USCS. Currently, Bob is a monthly LOG contributor and one of its fine officers.