I found some information
here about an unsuccessful attempt to bomb New York using zeppelins in August of 1918.
This is the first mention I've ever seen of an actual operational plan to do anything like that!
The ships were intercepted by a British fighter and never made it to NY.
Actually your source doesn't say that; it says that LZ-70, the alleged intended lead ship, was shot down on a separate mission (supposedly just before the three-ship raid to America was to be launched) and that another of the three was later shot down, the last one being one of the war survivors which was broken up by the Versailles regime afterward.
If they had bombed New York, what would the targets be and how many pounds of explosive would be dropped? Will we see another zeppelin raid against NY by the end of the war? As for long term effects, will we see more postwar effort put into developing zeppelin technology? I'm also thinking that the Treaty of Versailles would ban Germany from owning zeppelins, rather than simply prohibiting their construction.
Um. First of all--it's not that hard to believe that even a not-so-special Zeppelin like LZ-53 could have made it
to America, if it could evade British interception at the beginning. The British later flew one of their own, R-38 IIRC, across the Atlantic and back in 1919; that ship was a (modified) copy of earlier-model Zeppelins that had crashed and the Allies studied, and I presume was smaller than LZ-70. It was the first aircraft of any kind to cross the Atlantic east-to-west and the second of any kind to cross it at all, having been beaten by just weeks by Brown and Alcock flying west-to-east from Newfoundland to Ireland--they crashed their Vickers Vimy bomber on arrival however!
But the British rigid was just barely able to make it to Montauk, Long Island, before it ran out of fuel. (Their return flight to Britain was less dramatic and they arrived with plenty of petrol, since the prevailing winds favor west-to-east flight.) They flew pretty low, as the commercial Zeppelins developed by Hugo Eckener between the wars generally did, so they could carry a good load of hydrogen and thus carry more payload and fuel. The British ship did carry a goodly complement of passengers and crew. But no way could it have gone all the way to New York, dropped some bombs, and had enough fuel left over to make it all the way back to Britain, let alone starting from and returning to Germany!
So--I guess the German ships were all bigger, and could carry more fuel, and maybe even a small bomb load. Perhaps.
But first of all, the way the Germans did try (not always successfully!) to evade British interception was to fly very very high--so high, their crews suffered rather severely from both oxygen deprivation and cold. In order for these "height climbers" to reach Britain with a respectable bomb load and fuel to return home, they were lightened considerably, so that their structures were dangerously fragile at low altitudes. So in order to run the British gauntlet (and the Britons would not have to know the ships were on their way to America--they'd try to shoot down any Zeppelins they found) they'd either have to be height climbers, which would cut severely into their potential fuel and payloads despite the lightening of the hulls, or detour a very long way around the British isles, north or south. Either way, that offsets any advantage in size and superior design techniques that might have allowed the German ships more payload than the British postwar rigid. Not to mention they are starting from and hoping to return to Germany!
Second, they had severe problems with navigation, even for purposes of bombing nearby Britain. Among other things they did try radio navigation techniques, beginning with the risky measure of calling out themselves and hoping German ground stations could give them a fix before the British found them first, later developing systems of intersecting radio beams that didn't require them to give away their own positions. Obviously none of that would be any good approaching NYC! But aside from the fact that it was remarkably difficult to know where they were even flying in constant sight of land as they generally did, the big joker in the deck was weather. They never knew what sort of weather they'd be flying into. Again that problem is obviously much worse for a transAtlantic run!
Arriving at New York (and it might make more sense to simply bomb Boston instead since they'd get there first) presumably having avoided being noticed by anyone on the ground, I can only guess at their bomb load, but it couldn't be much.
Now on the other hand, the Americans wouldn't have much to intercept them with, even if they did have some warning. I'd think that AA guns of the type being more and more developed and deployed in Europe would be few and far between in America, since hitherto no one had the capability to attack. Same thing for airplanes of a type that could climb to intercept, and I suppose planes equipped with machine guns were few to nonexistent here. (The decision had been made to purchase what war planes the Americans would need in Europe where there were numerous manufacturers making tested state of the art planes, whose governments needed money badly and so would appreciate Americans spending theirs there, rather than on American made planes that might not be state of the art or even sound, and needed to be shipped across the Atlantic; the only planes being purchased by the American forces in America were trainers and a few experimental types).
This in fact would be the only way anyone in Germany could argue that Zeppelin raids were in any sense cost-effective; Peter Strasser and other advocates of Zeppelin raids did claim that by forcing the British to develop a whole AA infrastructure--spotters, spotlights, AA guns, interceptor planes--they did tie down a lot of men and materiel that otherwise the British would simply send to the front.
If a few tons of bombs dropped rather haphazardly on NYC (even unopposed, Zeppelins could hardly be precision bombers) or even Boston did panic Americans into diverting a lot of war funding to such infrastructure here, that would be mission accomplished I guess.
So, if the ships could get past the British gauntlet twice, and if they used really big Zeppelins that flew rather low and had good luck with essentially unpredictable Atlantic weather, I guess maybe they could hope to drop a few bombs on America, at least until the Americans did belatedly acquire some interceptors.
As I said upfront, I've never heard that this was an actual scheduled planned operation. I doubt a ship like LZ-53 could have been considered for it; I do know that Zeppelin people were working seriously on an "Amerika" ship design that was meant to do the job with a somewhat less desperately thin margin of error, and I doubt even the biggest ships actually built and flown during the war could do it, though the "Afrika-ship" (I forget its number, I want to say LZ-80? -85?) might have been able to make it.
So yes, it was an idea they had. I am very skeptical they were planning to actually do it with ships on hand, though I can see Peter Strasser perhaps ordering it, if the math did work out at least marginally for all three ships, as a way of trying it and inspiring the higher-ups to come across with the funding and priority demands for the bigger ships.
Had they done it, and kept at it, I imagine it would have been a matter of luck getting across the Atlantic at all--they could have the range, but the weather would be so unpredictable! And pretty soon Americans would be shooting down whatever ships did make it there, and made it past the British first; height-climbing would not be much of an option if they wanted to carry serious payloads, and the crews (and machinery!) would suffer badly trying to survive for days at very high altitudes (it was quite bad enough trying to hold on for 12 hours or so on a Britain raid). If they planned to fly the ocean at low altitude, the hulls would have to be strong enough to take the stresses associated with sea-level adverse winds, and thus they would not be able to climb as high even though their fuel would be depleted on approach to the American shore, thus would be very vulnerable to American defensive measures.
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Regarding your postwar questions--I do think that yes, such raids would probably tend to make Americans more interested in civil transAtlantic airship travel. To be sure their negative associations might offset the clear demonstration of capability! (If in fact your source is correct, and the Germans really did have this three-ship raid planned and nearly ready to go, the only reason I can think of I have never heard of it is that the post-war airship advocates chose not to mention it much, lest American investors be turned off by the idea that they too might have been bombed during the late war, or lest the story draw attention to how two of the three ships were shot down before the raid could happen...)
Versailles did indeed already forbid Germans to have Zeppelins, not just to build more. Eckener went ahead and built and operated some in defiance or blissful ignorance of the prohibition. The plan was to destroy all airship hangars; had the ones at the Zeppelin works been destroyed the company would have been dead in the water, quite unable to raise capital to make more even if the Allies later relented. For this reason, the company tried very hard to interest Americans (who were not signatories of the Versailles Treaty) in purchasing something from them; offers included the planned Amerika-ship. For a while Billy Mitchell was scheming to get one for the Army despite plain orders to do no such thing (the Navy was given charge of rigid airship development) and eventually the USN was authorized to get a rigid from Zeppelin; this was the LZ-126 Los Angeles. As the Zeppelin officials hoped, the American interest in building a new ship (and the failure of the Versailles powers to provide Americans with the old wartime rigids they were promised--the Germans having sabotaged a number of Zeppelins in their hangars rather than turn them over) did lead to American advocacy of a stay of execution, and by the time the Navy took delivery of Los Angeles, the pressure to destroy the construction hangars was off.
So--since it was American patronage that did save the Zeppelin hangars, I suppose if Americans were outraged enough, we'd join with the Versailles consensus and have them all razed early on, and any hopes for future airship development would have to be based on British or American projects.