The following narrative is from an e-mail sent by Art Shaw to Norm Hammond
detailing Art's duty as the last American to sail aboard the Thornback
Norm,

I entered the Navy in 1969, was in for 6 years, and most of my time
was spent at the Submarine Base in Rotten Groton.  I was enlisted as
a Communications Technician (CTM).  The M is for Maintenance.  All
the guys in our shop were CTM’s.  We worked for Naval Security
Group (an organization that was based on Nebraska Ave. in
Washington D.C., which was just disbanded a couple of years ago).  
Our shop dealt in specialized electronics, so we were basically ET’s,
but with a different mission than ships crew.  

I was selected as one of a 5 member team (two enlisted per boat, plus
a chief) to participate in a program to outfit the Turks with specially
equipped Diesel boats, build a laboratory at their submarine base in
Golcuk (on the south side of the Sea of Marmara – See Google Earth
shots attached), and train them how to use the equipment to help end
the cold war.  I was not a part of the product of our efforts, but I would
bet that the Thornback did its part in the Black Sea to end the cold
war.

Our team worked on two pairs of boats.  The last two were the
Pomfret and the Thornback.  I worked on the Thornback.  The
shipyard did many things, including overhauling engines, dry-docking
for hull repair, updating sonar systems, etc.  The Naval Security
Group interest had to do with gutting Radio, and installing 30 new
pieces of electronics in addition to the electronics that was already
there.  We cut away the ¼” steel shelf plates. Welded in new 19-inch
equipment racks, installed the new equipment, and trained the radio
crew how to use is all.  We also installed two racks of equipment in
the Sonar Equipment space below the Control Room (adjacent to the
pump room).  That equipment tied into the equipment installed in the
Radio room to make a larger system than could be placed in radio
alone.

I transited to Key West from New London to train the radio crew to
use the equipment under “at sea” conditions.  I was the only American
on board for this cruise.  The Turkish Navy has (or did at that time)
three classes of sailor:

-- The Subai (pronounced Soo-Bye), or officer.  The officers in the
Turkish Navy are managers of men only.  All officers speak English,
and speak it well.

-- The Asubai (pronounced Ass-Soo-Bye), or petty officer.  The petty
officers are the engineers and specialized technicians.  They are the
ones with the know-how, and are the can-do guys.  All Petty Officers
speak English, and were our primary interface.  These guys were
great!!  They did not know the meaning of “can’t be done”.

-- Oscaries (Pronounce Oss-Carries), or enlisted grunt.  These guys
were generally from poor rural families, spoke no English, were forced
to work 24 hours a day with no promised time off, no assigned
bunking (they had to sleep when they could, wherever they could find
a quiet place).  There was also no promise of food, and I never saw
any of them eat, but they looked healthy, so they were getting fed
somewhere.

The Thornback went to Key West for ASW training and torpedo
practice.  There may have been other Americans who rode the boat
on day trips to assist in this training.  I know the boat went out about
every day, but back in at night.  I rode out on several of these days
for additional training on the equipment under different conditions.  
Our team stayed in Key West during that month, and we only left to
go back to New London when the boats sailed for Turkey.  So to the
best that I can tell, I was the last American to sail a cruise from one
point to another (multiple days) on the Thornback.

Hope that answers a question or two.    

Cheers,

Art Shaw
Above is a Google satellite view of the TCG Uluc Ali Reis S-338 on display as a museum moored in Istanbul, Turkey