To understand why an airship is not some kind of oversized airplane, we find it is useful to make a direct comparison of the state-of-the-art for both airships and submarines circa 1928. Why that particular year, just before the worldwide economic depression? Several countries were pursuing both technologies, and at that point in time, great improvements had been realized from their humble beginnings. As we shall see in this page, it was the last point in history where the two technologies had approximate technological parity.
Well funded by Government contracts, the Portsmouth Naval Shipyard in New Hampshire between 1924 and 1929 designed and built five 381-foot V-class submarines. In the same time period the Zeppelin Works, funded in large part by donations, had designed a number of rigid airships, but following the delivery of LZ-126 to America, had completed only one.
Submarines require extensive dock facilities during construction. While most any dry dock large enough to encompass the sub can be used for later repair, it must be prepared with specific keel blocks designed to support the hull at structural member points. An airship needs only a big shed with few specific preps for a particular hull in either construction or repair. Generic stands to support engine cars and control car supplement lumber to support the keel, and cable hangers from the rafters. (During construction additional stiffening was also supplied by tying off rings to the hangar walls.)
USS Argonaut (V-4, later SS-166) was commissioned on 2 APR 28, with Lieutenant Commander W.M. Quigley as Captain. The V-4 was 381 feet in length, its beam was 33 feet 10 inches, and it could sprint at 15 knots surfaced, and 8 knots submerged. At the time of the construction, V-4 was the largest submarine ever built in the US. V-boats were exempt from the armament and tonnage limitations of the Washington Treaties by special agreement.
Graf Zeppelin (LZ-127) was christened on 8 July 1928, with Captain Hans Von Schiller as her senior commander. LZ-127 was 776 feet long and its “beam” (diameter) was about 100 feet. Like any airship, her ground speed was relative to the wind, allowing measurement of greater than ninety miles per hour ground speed with a favorable wind. She could do 60 mph in still air. At the time of construction LZ-127 was the largest airship in the world, but his very existence was only made possible following the Locarno agreements, which relaxed the devastating restrictions of the Treaty of Versailles.
The Argonaut featured a newly designed pair of diesel engines fed from large diesel oil tanks outside the pressure hull. Like earlier diesel subs, since the fuel was lighter than water, its consumption would have a minor effect on the sub’s condition of buoyancy. The Graf refined the five Maybach gasoline engines used in her predecessor with several experiments to ‘tune’ them for best efficiency. The basic fuel was a gaseous mix blended to exactly the same weight as air, so its consumption had no effect on the airship’s buoyancy. In a master stroke, the Graf’s designers actually turned the tables on gasoline’s dead weight. Instead of carrying excessive amounts of useless water ballast, the Graf used gasoline, its auxiliary fuel, for static trim. If the ship was leaning toward being heavy, engines were switched over to consume the necessary tonnage of liquid gasoline. Lightness could be addressed by flying into rainclouds to collect water ballast, or venting hydrogen.
V-4’s specially-built engines failed to produce their design power and some developed dangerous crankshaft problems. Since buoyancy was independent of engine power, the submarine was not lost during these trials. LZ-127’s engines, adapted marine motors, were the subject of experimentation for optimal fuel composition. Following improper bolt torquing, on one flight over the Atlantic an engine broke a crankshaft, followed by another and another and another, until only one engine remained – carefully – in operation. Since buoyancy was independent of engine power, the airship was safely nursed back to a mooring in France.
The Argonaut had twice the battery volume of earlier designs and included the first 240 volt electrical system, allowing for smaller onboard electric motors. The Graf was also wired for 220 volts, but it was fed directly to consumers from the generator room rather than having any notable battery capacity.
In January and February 1929, V-4 underwent a series of trials off Massachusetts. On a trial dive during this period, she submerged to a depth of 318 feet. This mark was the greatest depth which an American submarine had reached up to that time. V-4 would use the aforementioned depth finder to echo a return for measurement.
In August 1929, LZ-127 began a round-the-world flight that included a nonstop Berlin-to-Tokyo segment crossing the Stanovois Mountains above a challenging elevation of 5,500 feet. (During the Great War, Zeppelins operated above 15,000 feet and one exceeded 22,000 feet in an emergency. But the Graf was a heavily structured, luxury ship built to last.) The long-distance record set that year would stand for more than a quarter-century. Altitude was checked periodically by dropping empty seltzer bottles over the side and timing their fall until impact, but the Graf would later have a sonic altimeter to calibrate its barometric-based altimeter.
In V-4’s daily operations in the ocean, dives would be undertaken on a mostly daily basis to adjust trim and run salinity checks. The ever changing condition of the boat as well as the effects of the surrounding ocean had noticeable effect on the sub’s performance. Likewise, the LZ-127 carried instruments that advised its crew about changing atmospheric conditions, since the ocean of air and thereby the ship’s static condition was in constant flux.
To submerge, the Argonaut flooded tanks with seawater to achieve slight negative buoyancy, then slipped below the surface. When outside water pressure reached the point it could damage the inner hull, the sub could dive no further safely. To ascend, the Graf Zeppelin, cells filled with hydrogen gas, adjusted ballast to be slightly buoyant. Passing into lower pressure air on the way up, cell safety valves would open automatically and prevent overpressure. When the lifting power of the remaining gas operating in lesser pressure matched the airship’s weight, it could ascend no further safely, even if driven upwards with powered nose-up climb.
To surface, Argonaut opened valves from its compressed air supply (typically 3000 psi held in heavy tanks) into the ballast tanks, forcing out the seawater. Breaking the surface, the precious compressed air was then spared by coaxing out the remaining water with high-speed blowers. Induction valves were opened and the big diesels started, and immediately the high-pressure compressors (typically twin, four-stage) were clutched in to start mashing air back into the heavy flasks. This was nicknamed “jamming air.” The Captain had options as to which diesel would be used for each purpose. (Some subs had an auxiliary engine which could be fired up to run a generator to top off the battery charge.)
No airship has witnessed the creation of a compressor so light and powerful as to be able to affect buoyancy and still justify its weight and power demands. (A visit to a helium facility reveals the massive bulk of its hefty gas compressor and its light bulb-dimming power requirements.) To descend, the Graf Zeppelin valved hydrogen gas to achieve neutral or slightly negative buoyancy, then used engine power coupled with slight negative pitch to decrease altitude.
On the surface, V-4 could run her diesel engines to turn the props, compress air, and generate power to charge her batteries. In a typical WWII American sub, a battery cell was eighteen inches square and four and a half feet tall, capable of delivery 4000 amps. 125 cells connected in series delivered electromotive force at 250 volts to the motors. (The bigger subs had two such banks.) A regularly scheduled electrician’s watch insured constant monitoring of these batteries, entering the battery compartments and taking specific gravity readings particularly during charging. The charging process generated hydrogen, which in the confines of the poorly ventilated submarine, would instantly mix with air and if unchecked, would become vulnerable to any ignition source. Special vents carried the gas away while the process was monitored carefully. (In later subs the gas was captured in water to be carried over the side harmlessly, while hydrogen detectors sniffed for any gas that might have gotten away.)
Whenever LZ-127’s hydrogen was vented to prevent cell rupture or to descend, the discharge was directed safely away through specially designed chimney-like vent stacks. The hull was also ventilated, to prevent covering rupture when rapidly changing altitude. This had the additional benefit of diluting and dispersing the constant hydrogen seepage that escaped through the cell walls.
Of course the Graf could run its air compressors anytime, the engine car tanks keeping a small supply for tasks including engine restart. The Argonaut’s diesels could not be reversed, but the airships’ gasoline engines could be. Designers refused to revert to heavy and bulky reversing gear transmission mechanisms in either vehicle. To back up, the submarine simply ran its electric motors in reverse. For reverse thrust, the airship’s Maybach VL-2 engines would be stopped, an engineman on duty pulled a lever to reverse the cams, and then compressed air would be used to re-start the engine in reverse.
Unlike a battleship’s gun operator or submarine’s “green board” indicator all is ready to operate, an airship depends on a checklist to safely ascend. V-4 could re-submerge as soon as it had compressed enough air for the return trip. If it were to lose compressed air it would not be able to return to the surface. LZ-127 could re-ascend by dropping water ballast weight, or consuming heavy liquid gasoline carried for the purpose. Once all ballast had been dropped and the airship was still negatively buoyant, it could not re-ascend statically until its gas was replenished at a station or tending vessel.
Neither type of ship was able to maintain perfect equilibrium at all times, nor was it necessary. Submerged, the submarine’s planes were used make minor pitch adjustments in the forward motion to maintain a desired depth. Likewise, over a small range of conditions, forward speed over the aft control surfaces allowed maintenance of cruise altitude of the slightly heavy or light airship. To make rapid changes in trim, for example in a crash dive, crewmen could be rushed forward to change trim. On the Graf these off-watch supernumeraries were nicknamed “Galloping Kilos” and were routinely scrambled along the keel forward or aft. On later ships that recovered water ballast in flight, men would still be sent forward or aft for rapid trim adjustment, while waiting for the water pumps to catch up moving ballast fore or aft.
For drinking water, American submarines boasted distillation units (typically Kleinschmidt) to separate salt and other undesirables from sea water. Of course there was never enough of the product, and manning the evaporators was hot, miserable work delved out as punishment for those foolish enough to waste fresh water. This single-distilled water was good enough for typical consumers in the sub, but a second purifying cycle was necessary to achieve the near perfect purity needed to replenish battery water lost during operations.
Likewise on larger helium-filled airships, water recovery equipment reclaimed water produced in the combustion process by cooling the exhaust and collecting the condensed tail-pipe drippings into tanks. In this manner the tonnage of gasoline consumed would be matched by tonnage of water recovered. The dirty hydrocarbon fuel made a sooty mess of the pipes, and cleaning them was handed out as crew punishment.
LZ-127 avoided this weighty complexity by the aforementioned use of gaseous fuel. To save having to wastefully valve hydrogen – it was cheap, but not free and necessarily available – later ships would be run into rain clouds to collect water in their “gutters.” When enough tonnage had run into the tanks, the ship could continue on course. (Smaller airships could not afford the weighty complexity, eventually hitting on the idea of throwing a bag over the side and winching in some seawater ballast, to be put into empty dual-purpose gasoline/ballast tanks.)
With the interior always warmer than the surrounding sea, the submarine hull would be cooled well below the dew point. Moisture forming on the hull interior would drip into and onto everything constantly, an annoyance in early submarines that turned to outright danger with increasing interior electrical complexity. Interior air was circulated through a de-humidifying air conditioning compressor, and the extracted water collected into a tank which provided water for bucket baths. Old hands had learned to draw the water off early, before the sweat, fumes and stench of extended dive times soaked in.
Fuel tank ullage providing a bomb-like environment for explosion was a worry in most vehicles. Worse, in submarine fuel tanks water pressure would crush an emptying tank. Since seawater is heavier than petroleum, fuel was drawn off the top and seawater was allowed to fill in below. (Some subs used convertible tanks that, in addition to fuel and water, could also hold air so the boat would ride higher in the water and be capable of greater surface speed.) Likewise, there was very little explosive ullage in the totality of Graf’s small number of aluminum gasoline tanks. The bulk of the Graf’s gaseous fuel was stored in fabric bladders occupying the lower one-third of the airship’s volume. As the fuel was consumed, the bladder would shrink, leaving very little space for air to mix in explosive proportions. Air, filling in the void between lift cell and fuel gas cell, was exactly the same weight as the disappearing fuel, so the ship did not loose weight as gaseous fuel was burned off.
The Argonaut could leave its pen and travel thousands of miles to a suspected target area. If nothing was found to shoot at, the submarine had endurance to patrol for additional days waiting for something to come along. Likewise, the Graf routinely left its shed in Germany, changed seasons as it crossed the Equator, and traveled thousands of miles. Once finding his landing area in the midst of a revolution, the Graf had to loiter in the air for quite a time awaiting the outcome. In more routine trips, the remote base in South America had only a fixed mast and basic facilities, yet it would be adequate to support Graf for most of the 144 times he crossed the Atlantic.
A surface vessel configured to resupply the boat, called a submarine tender, could re-provision and refuel the sub for additional patrol in a remote area before it would have to return to its base for maintenance. The Americans had demonstrated the converted tanker USS Patoka’s ability to support an airship for better part of a month’s remote deployment. The Germans had demostrated a similar plan for the Graf in model form.
Outside air temperatures aloft usually made for cold flights on the airships, but on the ZRS the crew’s comfort was attended to. A large belt driven fan below the engine room ran volumes of air across the engine’s hot exhaust manifolds to make engine room work more tolerable. In a forward engine of the ZRS ships, the hot air was ducted to the crew space and bridge. On the later German ships, hot air was ducted through channels doubling as secondary structure – table legs, for example, on the LZ-129.
Submarines smaller than the V-4 were equipped to carry small float planes in waterproof hangars. Surfacing, the airplanes could be assembled and launched for scouting or other actions. The LZ-127’s smaller predecessor, the USS Los Angeles, was equipped with an airplane handling device and successfully launched & recovered hook-equipped airplanes in flight. Originally envisioned as seaplanes for obvious reasons, budgetary restrictions never allowed even an experiment of this technology in the form of a sky-hook equipped floatplane.
More important than any technological similarities, or mirror imaged theories of operation, was something much less obvious: crews’ camaraderie. A ship of the fleet, authorized by Congress, christened in a ceremony, given a name and a sponsor, has a crew that calls it ‘home.’ The stressful, strenuous jobs are divided into watches, so the ship can operate 24/7 indefinitely. Each crewman has a job to do, but when off duty, he’s still on board. Getting off the boat is the temporary condition, as opposed to the temporary nature of a noisy airplane ride. It is the exception; the disposable craft’s mission is to be endured, followed by returning ‘home.’ Until you have been part of a ship’s crew and pulled your share of the load, it would be difficult to relate why some soul-less mass produced airplane (or even interchangeable blimp, requisitioned like an automobile or office chair) could ever develop the crew camaraderie found in a submarine or a rigid airship.
A crew that might call their corpsman their “penis machinist” could have been found in either vessel above or below the ocean surface. Such a crew gets to know what they need to do with a greater intensity than temporary operators of vehicles – and they tend to pull each other through the rough times.
For the few decades in our history where the sub and the airship traded places for technical superiority, there was this one point where the two were nearly an even match. Had the LZ-127 been mass-produced to make a fleet of anti-submarine ships, its crew could have rotated watches for days aloft trying to locate a sub, whose crew was rotating watches trying to avoid detection – to the full extent of their battery life. Directed by expected intelligence information, and equipped with even the rudimentary hydrophones and depth charges of ten years earlier, the Graf Zeppelin would have been more than a match for the Argonaut.
Graf Zeppelin almost had one opportunity to find a submarine. Despite its impressive scientific achievements, the Graf’s eight-day, 8,142-mile polar exploration flight is hardly recognized. (The submarine did not make it on time, but that was only on the wish list.) The ill-fated Italia polar airship flight is far better known and even Hollywood-ized. One historian observed, “Had the intended meeting at the North Pole between the Graf Zeppelin and Wilkins’s submarine taken place, this might be remembered as one of history’s great flights.”
Likewise, the yellow journalism that constantly reinforces the negative stereotype of the impractical, dangerous rigid airship is never going to appreciate the most successful airship of all time – the LZ-127 Graf Zeppelin. As such they will never ask why he was.
As Alexander the Great observed, “What a horse they are losing for want of skill and spirit to manage him.”