About the ZPG-2N Anti-Submarine Blimp

US Navy vs. Soviet Submarine Threat

Me flying in a ZPG-2N airship ("blimp") at the radar in 1954 out of Lakehurst Naval Air Station, New Jersey. The "Cold War" was going on then, and the U.S. Navy submarine service was upgrading the airships and submarines.

 Larry Rodrigues 1953.

The latest submarines were called "GUPPY" type (GUPPY: "Greater Underwater Propulsive Power"). Deck guns were removed, the outer hull was streamlined, the conning tower replaced by a sail, propellers were redesigned, more air conditioning added, and the battery capacity was doubled.

Guppy submarine

Most significantly, a snorkel was added to enable the diesel engines to take in air while operating at periscope depth. This reduced the radar target area to only the periscope, exhaust pipe, and snorkel air intake.

Submarine running on snorkel

These innovations allowed underwater speeds to exceed surface speeds. To save battery power, the diesel engines with the snorkel were used as long as possible to travel and make attacks. After the attack, they would use only battery-powered electric motors to escape quietly and deep.

At the same time, the Navy anti-submarine forces were infused with many new weapons to hunt and kill the latest "enemy" diesel-electric "guppy" type subs. One of the U.S. Navy's new anti-submarine weapons was the ZPG-2N airship made by Goodyear Aircraft Corporation. It was the end design containing all the latest electronic equipments and airship best innovations learned from earlier blimps. The Navy purchased five of the ZPG-2N airships.

Our Mission: Train and Learn to Use Full Capabilities of the ZPG-2N for Anti-submarine Warfare

Preparations for mission

Since I was well trained in all our types of Navy aviation electronics equipment operation and maintenance, I was assigned to Combat Air Crew 304 as an Aviation Electronics Technician. Our crew consisted of 18 highly trained officers and enlisted men. On long flights, we operated as two crews, each one on and off duty 4 hours rotating around the clock. Our training flights often lasted 20 - 30 hours (50 hours one time).

The training and practice exercises took place out in the Atlantic Ocean with a task force consisting of an aircraft carrier, a submarine, and several ships. Each planned exercise lasted several hours and consisted of the submarine using different tactics simulating attacking the ships starting from approximately 20 miles away. Our mission was to use our electronics equipment to search for and find the submarine, and then use various tactics to stop the sub attack with different simulated weapons such as a rubber-nose torpedo or small explosive depth charges.

Our Electronic Equipment

The primary initial searching electronic equipment was the APS-20 radar. We could easily see the surfaced submarine out to 20 miles or more, depending on our flying altitude.

At the start of the exercise, the sub would submerge to periscope depth and speed in some direction using the diesel engines and the air-intake snorkel sticking a few feet out of the water. The snorkel was a very small radar target 15 to 20 miles away! It was extremely difficult to pick out the snorkel target in the rough seas where the waves also made radar targets appear. The trick was to watch for a target that appeared consistently in nearly the same place, since wave targets were scattered randomly on the scope.

Radar scope imageWe flew a few miles behind or ahead of the ships so their targets were easily visible out of the "sea clutter" radar echos bouncing up from directly below us (center of radar scope).

Combat Incormation Center plotting table

When we detected the sub snorkel or periscope on the radar, it was reported to our Combat Information Center (CIC) officer and the plotter person. In those days, our high tech plotting board consisted of a round horizontal Plexiglass covered table with a light underneath and tracing paper on the Plexiglass. The table was set up like the radar scope with range marks on the Plexiglass that showed through the paper. By marking time and position of sub and ships on the paper, a record of the exercise was maintained and kept for later review. This was a crude setup by today's standards with computers, but at least we never had to stop the "war" because the "computer was down".

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When the sub's snorkel or periscope was identified on the radar scope, we headed for the sub at top speed - about 65 knots. That is about 75 mph or 120 kmh. When the sub detected us approaching, the sub would shut down the diesel engines, dive well below the surface, and operate on battery motors. Of course, the sub would take evasive maneuvers below the surface, and we would not know exactly where it was headed. But we had a good idea within a half mile, so we went there fast to where the sub was last seen on the radar.

ZPG-2N on operations over Atlantic.

After we arrived in the general area of the sub's last sighting, we dropped a circle of sonobuoys in the water where we thought the sub might be. The sonobuoys were about 3-foot long by 6 inches in diameter and floated upright in the water. When they hit the water, an antenna popped up (it was like a steel tape measure), a hydrophone (an underwater microphone) dropped down on a cable, and the saltwater batteries activated a radio transmitter. We could tune a special sonobuoy FM receiver to each unique sonobuoy frequency and hear the underwater sounds from the hydrophone. Usually, one or more of the hydrophones could pick up the sounds of the sub's screws. Using the known location of the loudest sonobuoys, we could determine the sub's approximate location. If needed, we dropped more sonobuoys to get a better "fix" on the sub. This required the pilot to fly low and make very tight turns. It was scary but exciting as we raced against time.

ZPG-2N making magnetic detection search.

We then flew down very close to the water surface and operated our magnetic anomaly detector (MAD) electronic equipment. It could detect the presence of the metal submarine if we were close enough.

When we detected a magnetic signal from the sub on our MAD equipment, we dropped a bright yellow dye marker and white smoke-float on the water. We made a few more high speed, low altitude, tight turns to pass over the sub trying to get three good MAD contacts. On the third positive MAD contact, we dropped a homing torpedo or depth charge. Of course, they were nondestructive types. If we were close enough for a real "kill", the sub would release a big bubble of air. We usually were successful in intercepting the GUPPY type submarines before they targeted a ship in the task force, and we were very proud of our team efforts.

Magnetic Detection equipment signal.

Here is what the MAD chart recorder would show when we made a pass over a sub. The magnetic anomaly detection equipment was originally designed for geological studies, finding mineral deposits, and locating oil fields. It also worked very well for pinpointing the location of a submarine. On this recording, the small needle swings are noise and the big needle swing is a definite change in the Earth's magnetic field caused by the mass of the metal submarine.

Airships were an excellent platform for carrying the MAD equipment because there was very little metal close to the magnetic detector out on the bow (front) of the airship. One time I was just messing around with the MAD gear as we were flying low over the New Jersey pine trees, and I noticed a pretty good size signal. I thought at first that I had found oil in New Jersey! When I looked out the window to see what it was. It turned out that I had picked up railroad tracks and a train!

ZPG-2N Navigator position.

We practiced variations of this hunt and kill scenario for days at a time. Our missions were often 20 to 30 hours long. Each crew member would be on duty 4 hours and then off for 4 hours. Sometimes I got really burned out but the excitement kept me going. Sometimes our airship crew operated as a pure combat information center (CIC) to direct the operations of the ships. In this scenario, we would radio the aircraft carrier to launch some aircraft and we would use our radar to guide them to where we thought the submarine was running submerged. The aircraft would drop the sonobuoys and use MAD gear, but they could not do nearly as well as a blimp.

Sometimes blimps worked in pairs, with one operating as the CIC and the other blimp intercepting the sub and making the "kill". That worked better than using the aircraft from the carrier, which flew too fast to get down low and make tight turns.

The most fun was when our single airship and crew would do both the search and the "kill" with our homing torpedoes. Airships really are a better platform than airplanes for this type work. Our unofficial motto was, "We fly low and slow!" With all things considered, our airships and crews were the best weapon against the diesel/battery subs of that time.

In the air, I was both the electronics equipment operator and maintenance technician. Years later after I was in the Air Force I only did the maintenance work and the operators did the long hours of searching. Everyone is a specialist in the Air Force! In the Navy I worked hard, smart and long hours, but I got a lot of satisfaction out of making a significant difference in the end results of our operations. I worked on that radar so often that I had major parts of the schematic memorized. It had a million watts of peak power and was the best airborne radar available at that time. However, often it was either arcing and sparking where it shouldn't be, or it was completely dead from a massive burnout. Because of all that power concentrated in a small area, heat and arcing were a constant problem. Some components had to be changed about every 12 to 24 hours from burnout. Most of the radar equipment was under the deck. I spent a large part of my flying time down in the airship bilges working on --and cursing-- that contrary radar. However, it was a most exciting adventure for a young guy like me then!

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© Copyright 2002, revised 2014 by Lawrence Rodrigues
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