Well done, partly.
The best way to answer you is to quote the official SEAPOWER 2018 ALMANAC which covers the US Navy, Marine Corps, Coast Guard and Merchant Marine with all-inclusive aviation data.
"The NU-1B OTTER is the military version of the de Havilland Aircraft Co. DHC-3, a high-wing, short takeoff and landing utility aircraft. It is flown by USNTPS as part of its curriculum. The NU-1B was manufactured in 1956 and has been in service at USNTPS since 1966. The aircraft is equipped with modern digital avionics systems. The NU-1B has the longest operational history of any naval aircraft in the inventory".
"The X-26A FRIGATE is the longest lived of the "X-plane" programs and is based on the Schweizer SGS-2-32 sailplane. The X--26A was developed in 1967 by the U.S. Navy to train pilots in yaw/roll coupling. Four aircraft were originally procured. Two aircraft remain in service with USNTPS in support of its curriculum".
As an aside, I was just once TDY to NAS Patuxent River in the 1960s as part of the Navy's A-7 jet aircraft Board of Inspection and Survey trials. At Point Mugu we did the acoustical measurements asked by Pax River as well as the missile integration and launches on Mugu's sea test range. The A-7 Corsair II as well as the F-8 Crusader were dangerous aircraft on USN Aircraft Carrier flight decks.
Thank you for your input.