August of 1959, REQUIN reported to the Charleston Naval Shipyard in South
Carolina to be converted to the Fleet Snorkel configuration. On August
15, 1959, REQUIN was redesignated as SS-481. Conversion to fleet snorkel
entailed the removal of all of the radar equipment, modification of the
conning tower fairwater into a so-called "high plastic sail", a steel
framework surrounded by thick fiberglass (this was an offshoot of the
GUPPY program, in which fleet subs were streamlined and given fiberglass
sails to reduce weight topside).
Another modification which REQUIN received, this time originating from the GUPPY III modification program, was a hull-mounted "chin dome", a dome which consisted of a 36-transducer hydrophone array (This wasn't noticed until REQUIN was in drydock in Tampa, Florida in 1990, while she was being prepared for her move to Pittsburgh). Below decks, the radar equipment in the stern room was removed, with the remaining space being converted to crew berthing.
After conversion to the fleet snorkel configuration, REQUIN resumed operations as an attack submarine. Operating during the remaining 9 years of her commissioned career, REQUIN spent a good deal of the time operating off the Virgina coast. Interspaced with these operations, REQUIN also continued to make deployments with the Sixth Fleet in the Mediterranean. REQUIN also participated in exercises with various NATO and South American navies, including participating in UNITAS VII in 1966, a series of exercises with South American navies which included the circumnavigation of the South American continent.
REQUIN's last Mediterranean deployment came in 1967. Leaving Norfolk on April 4, 1967, REQUIN entered the eastern Mediterranean at the end of the month. A few days later, after completing a seriews of exercises with the Sixth Fleet, REQUIN received word that the US signal intelligence ship USS LIBERTY was under attack. Not knowing who or what was responsible, REQUIN's crew prepared to go to the defense of LIBERTY, but received orders to surface and head for Crete. (It later turned out that the Israelis had "mistakenly" attacked the LIBERTY and REQUIN's orders to leave the area came from the Sixth Fleet commander).
After returning from
the Mediterranean at the end of June, 1967, REQUIN began a long series
of local operations off the east coast of the United States. These would
occupy the last months of REQUIN's commissioned career, except for the
last week in May of 1968. Leaving port in her last deployment, aside from
local operations, REQUIN was part of the massive search effort for the
missing nuclear attack submarine USS SCORPION (SSN 589). After completing
this and other local operations, REQUIN began inactivation preparations
in October of 1968 and on December 3, 1968, REQUIN was decommissioned,
bringing to an end her 23 years of service to the US Navy.