A few years in the making... I started my first one back in 2010 but quickly gave up.
The designation for the N class went from ZNP-N to ZPN-1. Unfortunately the "N-1" ship was a testbed for which no real reference material exists, so I have opted to skip it in favor of the actually very successful N-2 design, known as the ZP2N-1 and later just as ZPG-2. These were the ultimate evolution of the ASW patrol blimp in USN service. Note the extended control car, which actually housed the engines (the props being driven via transmission). Note also the droppable slip tanks suspended above the control car - allowing the blimp to jettison its tanks rather than forcing it to pick up ballast seawater as the fuel ran out to keep buoyancy control. A powerful winch with a towing sonar is located aft as on the ZSG-4 and ZSG-5 airships. The large globe beneath the control car is a powerful radar that looked for submarine periscopes and snorkels.
The ZPG-2, this is ZPG-2 #5. By the time the "ZPG" designation came out, the airships were being identified solely by their serial number.
Later, the ZPG-2 design was modified to create the ZP2N-1W or ZPG-2W, which was an AEW&C (Distant Early Warning at the time) blimp. This concept had been trialled on the M-class blimp M-4 previously and found to be successful. A height-finding radar was mounted in a radome above the envelope which was accessible via a ladder from the control car. Later still, this design was modified into the ZPG-3W / EZ-1C airships (the largest non-rigid airships ever built) which I am currently working on and will hopefully finish soon.
Finally, the ZPG-3W. This was the largest non-rigid airship ever built. It's interesting to note that the radar performance from the ZPG-3Ws was far better than that provided by an AWACS plane or similar.