The typical writings about the German army on the Eastern front at the end of 1941 focus on the harsh winter weather and insufficient winter equipment (clothing, lubricants, skis).
There was much more of interest, and of greater consequence, and I'm motivated to write a list of pointers for those interested in military history:
(1) Loss of mobility
(1a) Horses
Horses were still the No1 means of moving supplies and artillery pieces in 1941-1945 in the German army. According to different sources 600,000-750,000 horses were used by German forces on the Eastern Front in the summer of 1941.
Infantry divisions had lorry units to move supplies between railheads and the division, but horse carts hauled the supplies from the division's supply points and carried them till their consumption.
The horses were fed inadequately with oat because supply with oat was very demanding (large volume) and distances to railheads (incompatible rail lines) were often great. Most horses became exhausted within weeks.
Great many draught horses were lost during OP Barbarossa and had to be replaced with Eastern European horses; hardy, lighter - and weaker. Many smaller, lighter carts had to be used to match these different horses, and the quantity of drivers required rose.
I didn't find statistics on German horse losses during 1941 alone, but apparently 179,600 horses died mostly due to cold and hunger from 1st December 1941 to 15h March 1942, with only 20,000 replacements during this period. Replacements arrived later till May, but 60,000 replacement horses arrived in poor shape after long land marches during winter time and 118,000 horses were commandeered in Eastern Europe - almost all of them more hardy, yet also weaker. They were useless as draught horses for artillery pieces and the German standard heavy steel frame wagons.
Light motorcycles excelled in pre-war competitions employed by skilled drivers for a few hours, but within weeks of OP Barbarossa's start the light motorcycles had proved to be failures in army use. Many civilian motorcycles were lost as well, and only the expensive heavy military motorcycle types (mostly used with sidecars) were judged to be really robust. Their losses were severe because of their use by combat and reconnaissance troops, though.
Within the first five weeks 9,100 motorcycles were lost, yet only 606 were replaced with production or captured vehicles. The motorcycle rifle troops (Kradschützen) that had added crucial infantry support to tanks and motorised reconnaissance troops were ruined quickly.
Later on the nominal motorcycle strength (mostly for messengers) of infantry divisions was reduced to cope with the shortages, but the motorized infantry had to be converted to trucks and would receive substantial quantities of protected half-tracks only after 1942. The successful 1939-1941 model of fully motorized divisions combined arms combat had to change and adapt.
Within the first five weeks 9,100 motorcycles were lost, yet only 606 were replaced with production or captured vehicles. The motorcycle rifle troops (Kradschützen) that had added crucial infantry support to tanks and motorised reconnaissance troops were ruined quickly.
Later on the nominal motorcycle strength (mostly for messengers) of infantry divisions was reduced to cope with the shortages, but the motorized infantry had to be converted to trucks and would receive substantial quantities of protected half-tracks only after 1942. The successful 1939-1941 model of fully motorized divisions combined arms combat had to change and adapt.
(1c) Cars
The German army was mostly using civilian cars. They were hardly ever used for combat or reconnaissance roles anyway, so a reliable car for marches on unpaved roads was adequate. The use of civilian cars led to a horrible range of vehicles serving next to each other in a division. The repair shops could not possibly have adequate spare parts for these vehicles. Furthermore, many cars proved to be inadequate under the harsh conditions of the Eastern Front.
The Heer lost 21,559 cars during the first six months of OP Barbarossa, but production was a mere 3,089 cars. The losses were replaced with commandeered used civilian cars, which mostly represents a loss in quality.
(1d) Lorries
Many light and medium lorry types - Ford lorries with two-stroke engines, Czech lorries of all kinds etc. were found wanting if not entirely useless under the conditions of the Eastern Front. Attrition was severe by crashes, wear and combat actions.
The Heer lost 36,189 lorries during the first six months of OB Barbarossa, but production was a mere 12,139 lorries. Only 4,913 Soviet lorries (mostly light ones) were captured. Again, commandeered used civilian trucks had to be used.
(2) Anti-tank inadequacies
About half of Soviet tank production were still light tanks that could be defeated with a 37 mm gun, but those were mostly attached to rifle divisions and similar formations of the line. The mechanised formations for the main effort actions were (also) equipped with T-34 and KV-1 tanks. Adequate guns and munitions for their defeat were introduced in substantial quantities during 1942, but still in inadequate supply during the summer of 1943. The problem was in part that due to a tungsten production shortage Germany had to limit tungsten largely to tools production for metal works. Without tungsten projectiles the range of 2.8, 4.2 and 7.5 cm squeezebore anti-tank guns became useless. The tungsten could not be replaced with in their projectiles because the whole point of these guns was to have the penetrator impact at very high velocity (~1,200 m/s). Steel penetrators shattered when impacting on hardened steel plates at such velocities. New, conventional anti-tank guns of adequate power had to be introduced, and later on shaped charge munitions arrived especially for the infantry and stub guns.
(3) Infantry weakness
Infantry casualties were severe in Russia. German infantry divisions had a replacement battalion for training, but they would have needed a replacement regiment to sate their need for qualified infantrymen. This wasn't feasible for lack of trainers even if it had been attempted. Another problem was that the politically well-connected (Göring) Luftwaffe drew unnecessarily large quantities of young, potential infantrymen conscripts and did put them into poor use (such as air observers in France). The Waffen-SS's recruiting of particularly fit young men and subsequent waste by inappropriately aggressive tactics was another problem.
The German infantry strength on the Eastern Front of 1942 was approximately half of what had been available there in 1941.
(4) Armoured reconnaissance
The skilful employment of fully motorized divisions requires sufficient reconnaissance. The divisional armoured reconnaissance troops were meant to deliver this, but they depended on few armoured cars that were not very suitable for Eastern European terrain and on motorcycle infantry troops. Light (4x4) armoured cars were a disappointment on the Eastern Front and heavy ones (8x8) were astonishingly expensive. Some reconnaissance detachments were down to 11% of armoured cars and 50% of soft-skinned vehicles by November 1941.
Reconnaissance detachments of fully motorised divisions would later (about 1943) receive cost-effective light half-track vehicles for the Eastern Front, but at the end of 1941 and during 1942 their capabilities were very much reduced because of high attrition rates (when employed) and a shortage of suitable vehicles.
(5) Junior leadership
Officers from 2nd lieutenant (Leutnant) to captain (Hauptmann) faced severe attrition rates (life expectancy at the front measured in weeks) because they frequently led their troops instead of directing them from behind. Higher officers did the same, but much less often. The high attrition rates led to less experienced junior leadership and thus less skilful junior leadership. Officers who had seen Poland, France and months of OP Barbarossa were replaced by lieutenants with little leadership experience, if any substantial combat experience at all.
(6) Air support
Quality and quantity of air support was dropping as well due to attrition rates and demands of other theatres of war. The Luftwaffe's shortage of aircraft mechanics was severe.
Meanwhile the Soviets were in the process of replacing lost biplanes with relatively modern monoplanes. The red air force was not considered to be a very important influence on the war in Russia until 1943 or even 1944 by German post-war authors, but the dwindling of German air power made Soviet administrative marches safer and quicker, and less often helped the German troops to overcome stiff resistance during advances.
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Summary: The German army that emerged after the spring rasputitsa of 1942 wasn't merely mauled by winter and the Soviet winter offensive; it had lost during the summer and autumn of 1941 what made it such an effective tool of warfare in the summer of 1941 and it was to never fully solve the problem of anti-tank defence in regard to quality and quantity at the same time. It had been blunted by the severity of combat, the harsh logistical conditions (rail lines first needed to be converted, roads were unpaved, dust damaged engines which had inadequate air filters) and the harsh winter climate.
This historical episode is still interesting as a potential analogy for the future because Western land forces didn't need to adapt to such circumstances during the Cold War of later, and would thus suffer from similar problems. We could trust our automotive industries to supply enough suitable vehicles as the well-developed American one did during WW2 already and horses have lost relevance, but the inability to maintain the proficiency of combat and reconnaissance troops and their junior leadership ranks in a demanding conflict with severe casualty rates is all but guaranteed. The weak infantry component of Western army brigades could be ruined within days of campaigning against a peer force. It's reasonable to expect a typical Western army brigade to be blunted by severe attrition of key equipment (such as radars, AFVs), reconnaissance troops and combat troops within a week or two, and return as a skeleton of support troops and soft-skinned vehicles for (slow) rebuilding. We might also see again what happened to American divisions in 1944: Inadequately trained support troops pressed into infantry units to compensate severe attrition.
S O
some sources:
"Vabanque", H. Schustereit
"Personenkraftwagen der Wehrmacht", Reinhard Frank
"Die deutschen Panzeraufklärer 1935-1945", W.Fleischer/R.Eiermann
"Das Handbuch der deutschen Infanterie", Alex Buchner
