Didn't we already discuss that? The Italians depend on coal imports, fighting Britain means they have no transport by sea available - and thus will soon be short on coal.
To counter that, the transportation net must be improved. My guess is that this already happens on a great scale, as these supplies need to be transported to Germany as well. With Germany getting coal mines in Belgium and France running properly, they might be able to export more to Italy. And once Russia is out, the Russians may sell coal (or deliver coal as part of reparations). Furthermore, Italy would have to stockpile coal. These are possible prerequisites of an Italian entry to the war.
As such, Italy will only join later in the war. Nevertheless, Italy joining the war is probably the easiest way to take out France...
That will be difficult.
There is a difference between a 100000 tons of vital supplies from Italy. And building an infrastructure for 1 million tons per month on the
hope that Italy might join the war on the CP side.
Germany is at war right now. To improve the transportation net that much you´d need additional steam locomotives, freight cars, rails and construction crews. And every single item used here will be missed by the German armies in France and Russia.
And the AH armies in Russia and the Balkans.
Would you divert so many resources just hoping that Italy might join? While every resource is desperately needed by the armies already fighting?
Okay, my sources.
I´ve found a map on the Internet detailing German railways in 1896 (for another thread in the past). The map also includes Belgium, the Netherlands, Eastern France, parts of Austria-Hungary, Switzerland and Northern Italy.
(I additionally checked the histories of the Swiss and Austrian railways to find out if more railway lines to Italy were built till WW1.)
Additionally I looked at my copy of "Rivers and Canals - History of German Waterways" (in German).
Existing possible routes:
Route 1: Ruhr region -> upriver the river Rhine to Basel (possible for smaller river ships unless really low water) -> Swiss railway over the St. Gotthard pass -> Milano (Italy)
Route 2: Ruhr region -> upriver the river Rhine to Karlsruhe or Kehl -> then by railway over Munich -> Innsbruck -> Bozen -> Verona (Italy)
Route 3: Ruhr region -> upriver the river Rhine to Karlsruhe -> then by rail to Regensburg on the river Danube (no steamships upriver of Regensburg) -> downriver the river Danube to Vienna -> railway transport over Villach to Udine / Padua (Italy)
Alternatively Vienna -> Laibach -> Trieste (the Austrian railway histories mentioned that a second railway to Trieste was planned before WW1, don´t know if it was finished).
Route 4: Silesia coal region -> railway transport to Vienna -> then follow route 3 options
Notice that in routes 1-3 I did try to make the most use of waterways. The cheapest and easiest way to transport something like coal.
Route 1 would have the shortest amount of railway transport involved. Roughly 200-250 km. But it involves the Swiss Alps and Swiss neutrality.
Route 2 would involve the Austrian Alps and a railway transport of roughly 500 km.
Route 3 uses the river Danube to circumvent the worst of the Alp mountains. It still involves roughly 400 km of railway transport.
Route 4 is wholly railway bound. Roughly 500 km to the Italian border.
Occupied Belgian and French coal mines would involve additional railway transport to Cologne on the river Rhine first. There´s also the question, who is "running" the mines there? I´m not sure if forced labor would be legal? And the German miners (the ones not in the army) are probably busy in the Ruhr region, Silesia and the Saar region.
Could Germany - without the use of probably illegal forced labor - divert 11 million tons of coal per year to Italy? Especially if Poles in Silesia might leave for independent Poland?
Now let´s talk about steam locomotives. One of the best pre-WW1 German ones, the Prussian P 8 "could haul 300 t at 100 km/h (62 mph) and 400 t at 90 km/h (56 mph) on the flat...".
http://en.wikipedia.org/wiki/Prussian_P_8
Unfortunately even if you circumvent the Alp mountains (route 3), the ground in Bavaria and in Austria isn´t exactly flat. And there will be domestic traffic on the rails too. Likewise not every part of the railway lines will be certified for 100 km/h (or 300-400 tons for a single train).
Loading and unloading time. Maintenance time. Resting time for the crews.
So in a best case scenario a train might make a one-way trip in a day. Return the next day. If you use the routes across the Alps too(route 1+2), a train might need two locomotives. More trains of course mean larger depots of water and coal too.
Pretty soon we´re talking about 300-400 locomotives at least. That´s 18% of the best German locomotives just for supplying Italy with coal. That´s the peace time production for 12-15 months.
In our Tl the existing steam locomotives were used to the "breaking" point. Which seems to indicate that producing new locomotives, even doing regular maintenance on existing locomotives was a low priority.
And notice too that using existing river boats (options 1-3) on the river Rhine (and river Danube) means that these boats can´t transport other goods. So you either need additional new river boats too or supply for someone else will get hurt.
Sending 30-40 trains to Italy per month to haul back the desperately needed 100000 tons per month supply is doable. Especially since these trains also carry some valuable German goods to Italy for further export to the USA, South America etc.
Preparing to expand it 10 times just on the hope that maybe Italy might join the CP powers seems ill advised though?
Keeping Italy neutral might really be the best option?