Certainly inspired by the balloonists of the American War Between the States and therein Lowe’s Army-standard wagon mounted hydrogen generator (photo), 
many major powers’ armies were fielding observation balloons by the late 1800s. Perfecting portable hydrogen production within its ballooning supply train, the “high ground” could move with the troops. Of course, it took precious time in a fast-moving battle to make the gas to fill a balloon. If the battle was near a town, Lowe’s competitors would fill their balloons from local gas mains (citigas was largely hydrogen) and the balloon would be pulled to the front.
By the turn of the century the British had developed a more compact wagon-mounted hydrogen production unit (photo), but it still took time for the chemical process to pump out the gas, while the battle front could be moving dramatically.
Under the leadership of Chief Designer of Army Balloons Col. S.E.B. 
Templar, Superintendent of Her Majesty’s Balloon Factory at Aldershot, the British Army was the first to field the art of compressing hydrogen, generated during quieter time in the backfield, into portable cylinders.
For the first time, in their war against the Boers (photo), the Observer Corps could rush the pressurized cylinders to the battlefront and erect a balloon to quickly check on enemy movements.
Col. Templar had later inspected the Spenser, Beedle and Barton airships and even found funding to begin construction of a UK government airship in 1902.
With streamlined private airships paving the way, militaries abandoned the spherical 
observation balloon. The major powers adopted the easier-to-handle sausage-shaped envelope. These sometimes-called “kite” observation balloons and their hydrogen generators were even taken to sea. Such observation balloons were in common use by the onset of The Great War (and were even in limited use in the next war).
By 1915 the evolving aero-plane was not suitable to replace the observation balloon, but by 
mounting a machine gun thereon, the enemy’s “eyes” could be effectively harassed. Early parachutes saved many a balloonist as airplane ball ammunition riddled his bag, which then had to be winched in to be patched or replaced. Eventually 
combatants developed “balloon buster” ammunition that, at the exit wound at least, could ignite the flammable envelope material. Even though the airless gas inside could not ignite, the flames spread quickly until containment was lost. This left plenty of time for the observer to “hit the silk.” When the Americans joined the fray, only one observer – LT Cleo Ross – was killed in the entire war, when the burning balloon fabric fell on his parachute.
Meanwhile, in the 1880s, British scientists in India had discovered the periodic chart’s second element did indeed exist. Since spectral analysis of the sun had revealed its presence there, so the logical name “helium” was selected for it. Decades later, trace amounts of helium were found in Canadian natural gas. Laboratory experiments had shown the gas to be “noble” – it would not readily mix with just about anything, notably oxygen. Since nothing can combust without oxygen, helium could, under just the right circumstances, act as a smothering agent.
In what some revere as a lucky accident of history, as the Great War expanded, someone in the UK wishfully concluded the flammable envelope might survive if it was filled with an inert gas. The list of such gasses is long, but most that are effective smothering flames are heavier than air. While twice as heavy as abundant hydrogen, helium was still much lighter than air. Could it be the answer to save observation balloons, they wondered? The British expended considerable resources to try and isolate usable quantities of the rare gas in Canada, but eventually gave it up as impractical. That would have been the end of it, since the US had elected a President that promised to keep Americans out of foreign wars.
Meanwhile, down in west Texas, residents using natural gas had been annoyed by typically having to make several attempts to light their stoves. Their cooking gas was contaminated with something that floated to the top and complicated ignition before it vented away. When America entered the World War, that uniquely rich concentration went from annoyance to industry. The US Bureau of Mines developed liquefaction facilities to extract the gas – code named ‘argon’ – from the its natural gas carrier. With the unlimited resources available in wartime to exploit the planet’s richest 
concentration (often bragged to be as much as 3 per cent), the BoM was on its way to establishing itself as the sole supplier of a brand new element. However, by the “eleventh hour” in November 1918, all these resources had managed to isolate, compress into portable bottles and transport just enough helium to fill but one observation balloon. The actual price of these pioneer bottles has never been calculated.
Though the Great War was over, the years of Allied toil and treasure could at last be evaluated, since an easily performed side-by-side test could be arranged. Hydrogen would be generated and used to inflate one observation balloon at the test site. The second would be inflated by plumbing all the Texas helium bottles together into a manifold. Then, with mannequins in place of real observers, airplanes would attack them both using their best “balloon buster” ammunition.
No such test took place. Nor has it ever taken place, to this day.
Evidently worried the extremely expensive world’s only isolated supply would leak out, no helium inflation of an observation balloon was made for decades to come. To this day, the massive resources expended have never been justified via an easily arranged demonstration – or in any other side by side test. The War than ended all wars was itself over; where was the need? Indeed, the BoM, it seemed, would have to “return to normalcy” along with the other war industries now out of a job. But, BoM wasn’t going quietly; “argon” no longer had to be kept secret. For them, it was time to go public.
In a 1919 National Geographic article, BoM’s G. Sherburne Rogers made the exciting revelation: “Helium, the new incombustible gas which promises to revolutionize the science of ballooning… and this country thus has a powerful advantage in the competition for supremacy in the air which the next decade is bound to witness.” The article is illustrated with a series of photos showing an 
balloon observer “hitting the silk” following an attack, as his smoking envelope loses its shape, then containment, then plummets to earth. The reader is expected to reach the conclusion first the lifting gas, then the envelope caught fire, without offering testing evidence proving same. Nor does article even mention the logistical nightmare of handling and plumbing all the gas bottles needed to fill even a handful of balloons – or that it had never actually happened.
In fact, a hydrogen balloon ignition test was sort-of performed, without the BoM being present. Don Overs wrote: “Augie O’Neil… spoke of hydrogen fire tests conducted at Wingfoot Lake after the loss of Goodyear’s Wingfoot [Air] Express … J. F. Cooper… conducted tests such as punching a hole in a hydrogen filled barrage balloon and lighting the escaping hydrogen. Cooper noted that the fire would not progress closer than a few inches to the balloon….” and that a slight disruption, in this case passing a hat in between, would snuff the fire. This action illustrated a simple fact: oxy-hydrogen fire cannot “back up” any more than the flame can ride back down you burner’s supply hose and explode your BBQ grill’s propane tank. It also showed that a puncture leak, even if ignited at the point the pure gas mixes with air to narrowly present a sustainable-flame oxy-hydrogen mix to an ignition source, did not radiate enough heat back to start a secondary ignition of even the flammable doped envelopes of the day. The test showed that if the “sparklet,” Brock, Pomeroy and/or other fabric-igniting incendiary rounds failed to ignite the envelope, the balloon would likely survive long enough to be patched and fight another day.
With all due respect to those who were convinced that, even if it could not prevent the doped fabric from igniting, filling the same balloon with helium would somehow snuff the flames, no such test was performed – nor has it been, to this day. (Many people would be astonished to learn of recent tests, made with hydrogen balloons made of non-flammable materials, not bursting into flames when shot with tracer rounds.)
Just in case someone might have questioned if Roger’s readers a difficult-to-see oxy-hydrogen fire had actually been photographed in the balloon attack, Rogers also played the trump card: explosion. Running another photo, of an Army observation balloon disintegrating and troops scattering, the reader imagines the horrible fate that surely killed them all. In fact, carelessness during a deflation had caused a visibly dramatic rupture; but there had been no serious injuries. (The accident report states the cause as improper grounding and allowing a gas-air mix pocket to form as the envelope deflated. It also states the one man slightly burned walked himself to the dispensary.)
Of course any compressed gas holds a potential hazard 
(photo: helium plant explosion aftermath) but the reader was not so reminded. Rogers capitalized on general public ignorance that fire and explosion are not interchangeable.
In addition to the three necessary elements of the fire triangle, to get an oxy-hydrogen explosive yield you also need somewhat robust containment. 
Since the level of air-in-gas contamination necessary for an oxy-hydrogen explosive yield is actually below that required to support combustion, explosion might seem more likely, especially during the deflation process. Indeed, we believe there actually was a oxy-hydrogen balloon explosion, once – about 15 years later.
On July 28, 1934, Army LTA men Kepner, Anderson and Stevens lifted off for an altitude record attempt. Having been improperly packed, their three million cubic foot hydrogen balloon began to tear at 60,000 feet. Valving and preparing to abandon ship as the vehicle dropped to 20,000 feet, the entire bottom of the balloon ripped away. The top retained its hydrogen, but racing downward, the gas in the dome became impregnated with air (increasing in oxygen as it dropped in altitude) ramming in. Electrical energy at those altitudes provided ample ignition sources. The report reads, “The final disintegration of the upper portion of the bag was caused by the explosion of the hydrogen-air mixture which it contained… A hydrogen flame is almost colorless and could not have been seen under the circumstances. Finally, it would not set the balloon on fire or even scorch the fabric. None of the fragments in the tests at the 
Bureau of Standards showed any signs of scorching.” The three men helped each other out of the capsule, then parachuted to safety, probably wondering why people later wrung their hands about the danger of ‘hydrogen explosions.’ The majority of the force was heading upwards, hence why the balloon dome was shredded. (Two would retire Generals, the 3rd as a Lt Col., without the media ever asking one of them why the hydrogen did not ignite the balloon fabric.)
The “Wonder Gas” article gave the reader the impression the BoM was ushering in a new bright future for “ballooning.” In the only hint that it was not all going to be perfectly rosy, G. Sherburne Rogers conceded: “The only apparent disadvantage of helium is the fact that it is about twice as heavy as hydrogen, 100 cubic feet of helium weighing 17.8 ounces and the same volume of hydrogen only 9 ounces… this is of little practical importance, the buoyancy, or lifting power, of helium being 93 per cent that of hydrogen.”
Seems simple enough – just make the balloon larger, then rape the hapless taxpayer to fill it. On the second Explorer attempt, deciding to use “safe” helium (though the balloon’s rip had nothing to do with the gas), the balloon size was increased to 3.7 million cubic ft., up from 2.5 of the first expedition. Then, when partially filled to erection, the new balloon suddenly ripped itself. A king’s ransom worth of the precious gas was gone in a flash of collapsing fabric, and with it, a chance to launch that season.
“Just make it bigger” was but the tip of a very large hidden iceberg, since even that much-publicized “7 percent loss” was less than completely truthful. And, as we shall see, when everyone forgot “ballooning” and motorized airships suddenly became the focus, that untruth became crippling… and deadly.
Navy Lieutenants Buckley and Barkley bravely published more unwelcome facts some years later: “It has been frequently said in print that helium lifts 93 per cent of what hydrogen will. This is approximately true at standard conditions (32 F., 29.92” Hg, 100% purity). But this statement is always ambiguously left hanging in the air, leaving the reader with the impression that a helium-filled ship will carry 93 per cent the pay (or military) load of the same ship filled with hydrogen. Actually, at normal operating conditions, the difference of the standard gross lift is more nearly 10 per cent due to the lower purity with which helium operations are conducted. But in substituting helium for hydrogen in an airship, the structural weight of the ship is constant, service load including fuel is constant (for the same range) and the entire loss of lift must come out of the only remaining variable – the pay or military load…The entire loss of lift reduces the military load by 50 percent, not 7 per cent, as we have been lead to believe.” As we shall see, BuAer genius C.P. Burgess calculated the loss to be 59%.
Not included as the cost per pound of lift, which is more difficult to calculate owing to the nature of the changes necessary for helium-based operations. So not only was the payload cut in half, but taxpayers would be paying more for less – a lot more. 
One of G. Sherburne Rogers’ photo captions admits that the typical 35,000 cu ft observation balloon, which had only cost $300 dollars to inflate, would then cost $4,000 to inflate. The caption also conceded the R.33, then the largest airship in the world, had only cost about $23,000 to inflate with hydrogen. Small wonder only four rigid airships would ever be inflated with helium – and of them, effectively only one flying at a time (with a single day’s exception). According to A. F. Simpson’s research, Army LTA expenditures for helium alone in 1923 were $668,500.00, when the previous year Army LTA entire appropriation had been $692,548.54! Smith continued, “As bad if not worse, it was expensive; so the operator was not only getting less for his money but paying more for less.” Teed echoed “…helium is 29.8 times as costly as an equal volume of hydrogen and only gives about 92.6% of the latter’s lift.” As Smith put it, all told helium lift cost 70 times the equivalent hydrogen lift.
In time of war the taxpayer can be shorn until even helium looks cost-effective, but aerostatic law was not so cheaply bought off. As Richard K. Smith explained, “Hydrogen cost about $3 per thousand cubic feet and airship operators were accustomed to taking off with their gas cells 100 percent full for maximum lift; as the gas expanded with altitude the airship’s automatic valves bled off the excess to the atmosphere.” LZ-127 Captain von Schiller echoed, “Consequently, the hydrogen cells are filled to capacity in order to create the maximum lifting power. It is really “lighter than air” and rises from the ground when released. But since the gas tends to expand under the reduced atmospheric pressure of the higher altitude, the gas cells would burst were it not for the over-pressure valves which let out the requisite amount of gas. Thus when the Graf Zeppelin rises to a height of 200 meters (the height usually chosen for reasons of safety), it must “blow off” 2% of its hydrogen, or 2000 cubic meters.” To replace 2000 cubic meters, one would have to order 290 H-type K-bottles of helium, if indeed that amount would be available in the time period’s allotment.
The solution? Easy! Just fill the cell(s) to as little as only two-thirds capacity (depending on the barometer and super-heat meter). Thus, you carry even less of the already-reduced payload to an even lower operating altitude! Burgess noted, “A further loss in performance from the use of helium follows from the necessity of starting flight with only partial inflation in order to avoid valving the costly gas as the altitude is increased.” A helium airship loosing 2% of its gas every launch was then, and is now, grounds for the treasurer-bookkeeper to assault a pilot-operator with intent to do bodily harm.
The greater nightmare came upon landing, after the fuel weight had been burned off. Smith 
continued, “If the airship was too light upon landing, the operator simply valved off gas to make her heavy enough for landing. Helium was a totally different story. In 1923 it cost $123 per thousand c.f.; and although this was reduced to $50 by 1929 and $25 during the 1930s, its price never became remotely competitive with hydrogen.” As we shall see, even taking off about one-third empty – and then still having to try to land “light” – caused their own deadly problems. As it turned out, these were just the most obvious problems with using helium in motorized buoyant craft.
Hoping National Geographic readers knew nothing of airship design, writer Rogers suggested with helium “…the speed and cruising radius of the craft may be materially increased.” But calculation showed just the opposite, Teed wrote. “the maximum length of full-speed flight of the airship is reduced 40.6%.” To understand why this huge difference – more than 40% – is factual beyond just what energy is lost by not using surplus lift energy as fuel, we must realize that hydrogen airships usually had the luxury of flying at equilibrium. Flying nose up for lift, or nose down to prevent an upward stall was the exception rather than the rule; with helium, it would be commonplace.
In his Design Memo #390, C. P. Burgess more fully detailed the additional, unseen problem. “Since the drag of an airship at any given speed is greater when flying heavy than when at static equilibrium, the gain in endurance by heavy take-off is somewhat less than the extra load of fuel divided by the hourly consumption when in equilibrium…from a combination of increased air resistance and diminished propeller efficiency when flying heavy… It appears reasonable to expect about 60% greater consumption when [required attitude gives a lift coefficient of 0.10 rather than at no lift at EQ] at any given speed. Furthermore, the increase in consumption varies approximately as the square of the heaviness.” Burgess concluded, “Fuel consumption is a minimum when an airship is in static equilibrium.” The NACA reached the same conclusion. “Any flight angle other than zero angle of pitch results in an increase in drag; hence more power and greater fuel consumption are required for an equivalent speed.”
“Just make it bigger” was not a simple modification, but rather a complete redesign. If the helium bag has to be much larger, the gasoline cans it lifts also much be larger and heavier to allow larger, heavier and more powerful engines to push the bigger lummox through the air at the same speed. So what to do, add even more power for the same speed, requiring even more fuel yet? It all adds up to less paying payload, less distance transported, less revenue taken in, at a much greater cost.
For the smaller ships in the inventory, switching to helium would prove not just crippling, but impractical. James Shock wrote, “The OB-1 was originally inflated with hydrogen, however on August 31, 1923 the Chief of the Air Service Engineering notified the commanding officer at Scott Field that the OB-1 was to be helium inflated. Test flights were made by Lt. Robert Robillard which proved unfavorable due to loss of lift (helium being heavier than hydrogen) and the control car had to be repositioned twenty inches forward to overcome tail heaviness. The airship also experienced reduced ceiling and endurance with helium. It was apparent a complete redesign of the airship would be necessary…” Now more difficult to control, there were two deflation landings. “The OB-1 was never reinflated and was declared surplus at the end of 1923.” The smaller Goodyear Pilgrim was loaned enough helium to make some trial flights, but the rare gas was expected to be returned when the experiment was over. Pilgrim quickly became a museum piece.
The operators’ universal message to the BoM in 1919: keep your helium to yourself. We don’t care it won’t mix with oxygen. We’re already keeping our lifting gas nearly oxygen-free, and we’d have to be even more careful with helium to prevent payload-robbing contamination. No, thank you!
So as more ships came on line in 1918 and the delivery of several designs continued into 1919 and 1920, the US military’s airships outdid each other to set altitude, distance, payload and endurance records time and again. Navy
“B” ships perfected a towed underwater microphone, dropped a torpedo, and helped perfect two-way airborne radio. (Photo: A motion picture camera goes aloft on a B ship, 1918.) Army and Navy “C” ships performed rescues and conducted research while traveling the country. The Army C-2 crossed America; the Navy C-5 would have crossed the Atlantic in 1919 for want of a stronger rip panel rope.
However, the men behind the would-be helium empire were not going quietly into the night. It came to pass no one would remember this entire effort was begun in the hope of saving observation balloons from incendiary bullets. The BoM would soon find an opportunity to expand their startup – and unwittingly hobble buoyant flight for more than a century.
Postscript:
Andrew Grey would later write about the ZR program in Air Power History, “The fate of the Hindenburg at Lakehurst more than two years [after Macon’s loss] obscured these prior disasters but in fact did no more than underscore the existing verdict against [rigid] dirigibles. There could be no such thing as a weather-proof dirigible lifted by helium, itself a structurally lethal ten percent heavier than hydrogen.”
Not surprisingly the Government never published statistics comparing the accident rate involving helium-lift vs. hydrogen-lift airships. It might not be considered fair, since obviously needing higher capacity and more complex gasoline systems would mean a greater chance of fire. Hence it’s hardly surprising that with the greater number of SS-type airships built, almost three times as many of the fewer number of K-ships built were lost with fire involved. However, remembering the original idea was to prevent envelopes from catching on fire, surely the enormous expenditure of lives and treasure could be justified when helium-filled envelopes would not ignite.
Hardly!
Even advanced postwar non-rigid envelopes burned just about as well as their silk predecessors and almost as well as the aluminum-rich rigid’s coverings. One “4K” bag ignited and burned 100% just preforming an air inflation test – no car or gasoline. In the photo, a ZSG2-1 envelope, ignited by a lightning strike at the mast at Glynco, burned completely in less than two minutes in spite of the fire crew’s best efforts, and the cats-&-dogs pouring down rainstorm!
However, the ultimate insult, the inevitable demonstration of helium’s failure to justify its original intention – that of snuffing envelope ignition when fired upon by the enemy – came on the night of December 5th, 1957. The accident got little press because no one was hurt, and the more Cold-war racy news of the Vanguard rocket explosion dominated the headlines (newspaper page here, highlighted story). The “5K” airship had inexplicably lost power in the Bermuda Triangle, and exhausted its batteries trying to restart its engines. The exercise was halted and the task group came to the aid of the floating but helpless airship. A destroyer stood by as the disabled blimp’s crew easily slid down ropes into the DD’s awaiting boats. Their DD sailor rescuers attempted to tow the valuable ASW asset, but had not been trained to do so, and the tangled line mess became unmanageable. Machine-gunning the derelict with ordinary bullets and tracer rounds, the helium-filled envelope suddenly ignited and burned completely in less than two minutes.
ZRS the movie itself will not need to enter the argument H2 vs. He. The film will reflect the fact rigid airshipmen knew they would be returning to hydrogen in time of war, since the operation of even just a few rigids – or even just one overseas – would absolutely depend on hydrogen, for several reasons.