In my article about the commercial bomber concept, I began my discussion of the idea that airliners could be turned into bombers in 1918, with the report of the Civil Aerial Transport Committee. But it turns out that it appeared some years earlier, though in a far more fragmentary and undeveloped form than in the interwar period. And it involved airships, not aeroplanes.
In December 1912, the Admiralty received a joint report from the military and naval attachés in Berlin about the wartime disposition and employment of Germany's airship fleet. They suggested that the German government was paying subsidies to airship manufacturers so that their civilian production would be built to the minimum standard required for military service. So, in the next war,
the naval and military authorities will thus have at their disposal not only the Government aircraft, but also a number of dirigible airships belonging to private firms fully manned and equipped and ready for instant service[.]
The attachés estimated that this would yield a German fleet of between 21 and 23 airships, though as it's unclear how many of these were civilian it's equally unclear how much of a difference their inclusion would make. But generally speaking, they increased the aerial threat to Britain:
A number of vessels in this formidable array of airships would be capable of sailing from Germany to Sheerness, Woolwich, or any other desired point in England and return without the necessity of an intermediate descent to the earth.
The commercial bomber idea also appeared in the press. 'C. C. T.' (i.e. C. C. Turner) , writing in the Observer at the end of March 1913, also attempted to estimate the size of the German air fleet in the event of war. He came up with 13 government-owned airships, and
In addition, there are in Germany privately-owned airships:--
So his total came to 23 airships, which corresponds well with the (presumably confidential) estimate provided by the attachés. This could be because they were working from the same information, or perhaps Turner got his figures from the Admiralty. The basic rhetorical function of the commercial bomber is much the same here as it was later, to inflate the size of the enemy air fleet and make it seem more threatening, the better to demonstrate 'the fatal complacency and ignorance permitted, and even fostered, in this country'. However, in the 1920s and 1930s, the commercial bomber idea was useful only so long as Germany had no air force, and more or less disappeared with the creation of the Luftwaffe (or so I argue). Here, it is being claimed that it is Britain which effectively has no aerial force to speak of, since it is credited with only 2 airships '(on order)'. So piling on even more German airships hardly seems necessary. Perhaps the point is to increase the German lead over France, which has 10 airships attributed to it '(these are less powerful than Germany's').
If Turner got his information from the Admiralty, he might also have taken the idea that civilian airships could be used for military purposes from the same source. But perhaps it was obvious enough: military airships and civilian airships were in fact more or less identical at this time. Schwaben, a DELAG airliner which first flew in June 1911, was built to the same plan as two military Zeppelins, Ersatz ZII and ZIII. Two other DELAG Zeppelins, Viktoria Luise and Hansa, were indeed pressed into military service in August 1914 after a rudimentary refit. Though they were mainly used for training, it seems that Hansa, at least, flew combat missions over France and the Baltic. And Sachsen, the last DELAG Zeppelin to be built before the war, raided Antwerp on the night of 25 September 1914. So as well as being the first commercial bombers in theory, airships might have been the first, and even the only, commercial bombers in practice.