I read somewhere online an assertion that US infantry divisions had more tanks than German Panzer divisions. Is this true? If so, why was the US able and willing to equip them with so many tanks (e.g. doctrinal reasons)?
I also read somewhere an assertion that US infantry divisions had many more trucks than German infantry divisions. Did this make them more mobile than their German counterparts? If so, to what extent?
I'll answer question 1 in a few sections.
I'll base this off of FM 100-5 editions 1943 and 1944, FM 100-10 (1943) and FM 101-10 (1943). Specifically this deals with US Operations, Administration, and Organization.
From what I can gather, organizationally, the US had accompanying supply trucks and larger divisions (the early ones having 2 light tanks and 2 mediums, and later divisions having 5 mediums if I remember correctly). As noted in FM 100-10 (1943)
An example of mobility is the reserve of supplies carried on trucks with combatant units; flexibility is secured by establishing regulating stations and distributing supplies laterally and in depth; security is obtained by taking advantage of the protection afforded by tactical units
The US logistical line focused heavily on mobility of supplies and the ability to use mechanized trucks.
Referring to the diagrams in pg. 8-9 in FM101-10 Infantry divisions in Square form) had accompanying Car Companies (T/O 10-277), Maintenance Corps, Engineer Corps and Platoons, and a Service Company of less than one battalion.
Although it was not as heavily mechanized as the motorized infantry division configurations, even the basic US infantry division had auxiliary motorization for transportation of supplies and necessities.
Compared to a Panzer Division (of which I'll sample multiple Panzer divisions, including the 1st, 3rd, 6th and 9th) a US infantry division was much larger, each having their own supply and support corps and companies. Logistically speaking a US Infantry division had more resources in general compared to a Panzer Division.
That said, to answer the second part of Question 1, the US was able to equip their divisions with that much material primarily because of how much more material the US had. For reference if we refer to the Armored Division in FM 101-10 pg 48-49 Diagram 20 we'll note a few things:
-Each corp had accompanying mechanized support companies.
-Each tank corps had accompanying maintenance and supply companies.
Sadly I could not find the exact distribution of Panzer Divisions so i'll need someone better versed in the Panzer division organizational details to fill in, however organizationally, it seems that the US composition was made to ensure that auxiliary forces and support structures all had mechanization. As to why, I would posit that the US' industrial capacity coupled with doctrine that was designed for the purposes of obtaining victory would motivate the US to provision their divisions and organizational scales as capably and sufficiently as possible.
Onto question 2:
Mobility was indeed an advantage of US doctrine. FM 100-5 emphasizes armored division capabilities of achieving victory through counter flanking and mobility, FM 100-10 in the "Supply" section emphasizes a quick transit of supplies and FM 101-10's organizational diagrams reveal to me an emphasis on not just mobility, but an infrastructure to ensure optimum uptime.
As to what extent, if holistically compared the US Infantry division ultimately was far more capable of re-supplying their own forces due to supply chains that reached beyond division capability and due to each division already including supply and support structures within themselves. Given that Panzer Divisions too had support companies for each corps, I'd wager that the difference in mechanization probably gave the US much more battle uptime as well as mobility.
But then again, this is only from reading the Field service manuals and comparing operational doctrine.
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