A Russian professional military newspaper recently published an article listing the lessons learned from Russian participation in the Syrian civil war. This war began in 2011 and is still not over. Among the lessons offered were that wars against irregulars, especially religious zealots, cannot be won from the air and requires well equipped ground forces using armor and other modern weapons. It was also believed that the United States did not attack and drive the Russians out of Syria for fear of starting a nuclear war. This was also believed to be the reason why other NATO countries did not support Turkey in Syria for fear of angering Russia. In general Russian leaders, if not the majority of Russians, believe their nuclear weapons prevented Western nations from getting involved in Syria other than by using airpower against ISIL (Islamic State in Iraq and the Levant) and in support of Kurds. Or something like that. The Russians appear to be ignoring local politics in the West and the Western aversion to wars like this in general.
Russia also dismissed the advantages of an air force using just smart bombs and guided missiles while at the same time bemoaning the fact that Russia had few of these smart weapons to use. It was recognized that the proliferation of modern portable anti-aircraft weapons (heat-seeking missiles) made low flying aircraft delivering unguided bombs prohibitively expensive in terms of aircraft losses. Thus many of the Russian airstrikes were in areas where there were few anti-aircraft weapons, like residential areas inhabited by pro-rebel civilians. For this reason, Russia believes artillery is still crucial in supporting ground forces fighting irregulars. Russia dismissed the ability of American cruise missiles to have a decisive impact on enemy forces. The Russian attitude was that low flying aircraft dropping unguided bombs was still effective if air defenses could be destroyed or otherwise neutralized. Russia believes numerous and effective air defense systems play a crucial role in neutralizing the effectiveness of enemy air attacks. This was a key Cold War doctrine that Russia still considers valid even though its air defense systems still prove vulnerable in practice. This has been happening in Syria but Russia believes somehow they will solve these problems.
Russia believes that EW (Electronic Warfare) can provide an effective defense against guided bombs but does not mention the improved effectiveness of INS (inertial navigation system) tech. INS has always been the backup system in GPS guided bombs. INS cannot be jammed or interfered with unless you apply a massive electrical signal to the smart bomb and disable INS. This has not yet been demonstrated in practice. Russia also recognizes their lack of radars or other sensors to detect low-flying (under 100 or even 25 meters) UAVs or missiles makes it difficult to detect much less destroy these low-altitude attackers. At the same time, Russia has already developed effective defenses against low flying armed UAVs, which have frequently been used to attack the main Russian airbase in Syria. Also not mentioned is the lack of defenses against Israeli missiles that go very high and then approach the target at a high (ballistic missile grade) speed. Russia also notes that Turkish use of armed (with laser-guided missiles) UAVs in Syria was very effective against ground targets. Russia believes airborne EW aircraft can neutralize many air defense systems, except for the manual (heavy machine-guns and portable heat-seeking missiles) carried by irregulars. Russia still believes its tanks and other armored vehicles are useful on the battlefield but not as dominant as during World War II and the Cold War.
The remaining lessons covered current problems. Russia can no longer afford a large, organized, trained and equipped reserve force. Russia has sought to organize traditional militias, like the Cossacks and believes this might be the way to go. Another difficult problem is the lack of large stockpiles of ammunition and heavy weapons. These were present during the Cold War but are gone now. A large reserve army, without a lot of heavy weapons stockpiles, was crucial in winning World War II but even that is more than Russian can afford now. Nor will the population tolerate compulsory reserve service.
Russia also noted the usefulness of aircraft carriers for distant operations. Russia had only one carrier and it was only sent to the Syrian coast a few times. The 14 carrier aircraft onboard flew 420 combat sorties but their effectiveness was limited by pilots lacking sufficient experience to be as effective as land-based aircraft pilots. Russia also noted the importance of pilot training and skills development, which many Russian pilots acquired in Syria, not before they arrived. Russia cannot afford the cost of sufficient training flights and paying for all those combat sorties in Syria has been a strain on the defense budget.
The article also noted the lack of Russian shipping or air transport reserves. Many Western nations have such capabilities and the Western air reserve fleet is particularly formidable. With these systems, legal and financial arrangements are made in peacetime to mobilize and use commercial shipping and air transport for military use in an emergency.
The article includes a number of instances where Russian conclusions differ from Western ones. Some of those differences are self-serving. Russia cannot afford the quality and quantity of military tech developed and used in the West. The article did not discuss the fact that China was emulating Western practices, not Russian ones and was the more immediate threat to Russia. That lesson is ancient and more imminent than ever before. But it is an official policy in Russian to ignore the threat in the east and concentrate on the imagined threat in the west (NATO).