US NAVY
The first entry is the original configuration (i.e. "as designed"). Only two ships were built like this: AVP-10 USS Barnegat and AVP-11 USS Biscayene. The main feature is the heavy crane for handling seaplanes: the same kind as on the large seaplane tenders of Currituck class.
AVP-10 USS Barnegat in 1942 wearing Measure 12 (modified) camo.
The third and fourth ships of the class - AVP-12 USS Casco and AVP-13 USS Mackinac - were built with a semi-fixed crane and 1.1" gun on the fantail.
The rest of the seaplane tenders were built with smaller light cranes (later on the first four ships received them too). Armament was considerably increased although it differed from ship to ship. Here's AVP-21 USS Humboldt in August of 1943 with a third 5" gun and a quad 40mm Bofors aft as well as two twin 40mm Bofors amidships.
Another example of the increased armament: two 5" guns aft on the AVP-22 USS Matagorda in September 1943.
AVP-33 USS Barataria in 1945 during the Philippines campaign. She's carrying extra stores and a boat aft instead of additional armament and wearing Measure 32/2Ax camouflage.
USS Abescon was built as a catapult training ship; a standard USN catapult was fitted behind the funnel and a pair of aircraft handling cranes on the fantail. She was used to train naval pilots to take off of the catapult.
Four ships of the class - Mobjack, Oyster Bay, Wachapreague, and Willoughby - were built as motor torpedo boat tenders. Here's USS Oyster Bay in 1944.
USS Onslow and USS Floyds Bay during the Korean war with new SU radars and rearranged armament aft.
After the war three ships of this class - USS Duxbury Bay (AVP-38), USS Greenwich Bay (AVP-41), and USS Valcour (AVP-55) - served as flagships in the Middle East.
In the 60's they received new masts, electronics and modified superstructures. In 1965 USS Valcour was reclassified as Miscellaneous Command Flagship (AGF-1).
US COAST GUARD
In the late 1940's US Coast Guard has acquired 18 of the Barnegat class ships from US Navy forming the Casco class.
Here's WAVP-384 Cook Inlet soon after the transfer and some modifications.
Another stage of USCG modification: the crane has been replaced with a mast (plus several minor alterations).
USCGC Bering Strait (WHEC-382) during her Vietnam War service:
FOREIGN USERS
A former Barnegat-class ship serving in Marina Militare as a special forces support ship:
Bering Strait in the Republic of Vietnam Navy service:
Planning on drawing:
- USN amphibious force flagship
- USN survey ship
- USN oceanographic research ship
- US C&GSS research ship
- USCG training cutter
- USCG meteorological cutter
- Norwegian training ship
- Ethiopian training ship
- North Vietnamese frigate
- Philippinean frigate
- Greek civilian cruise ship
Always a pleasure looking at your works WhyMe 
Thank you Kim for the crest