Soviet Union Overview
The soviet union focuses on mobility, rather then brute force, but they do have some heavy wepons for times when being fast is just not enough. This is focused by the starting force of the soviet faction - a rifle squad, a commisar squad, a maxim HMG, a mortar and 2 trucks in addition to the normal storage, 2 AA guns and 2 AT guns for every faction. The soviets are the only faction to get transports right from the start, allowing them to use the maxim and mortar to fortify a single position on the map of thier choosing.
On the other hand, the soviets begin with no production facilities and no ability to make light vehicle yards or air stations - only the three basic constructors fom a builder squad. Even the storage and AA start packed up and ready to move to another land, easely allowing you to put your base anywere you wish - not just the starting boxes. Usually your first action is to make a barracks as fast as you can, because the mobility advantage you get dissapears very fast.
After your barracks, the fun is not over, as your infantry has a hard time spreading communism over land, you will need to make a hard decicion: use your builders for more buildings, or capture flags with them. At this point, you're at a technology disadvantage, as your enemy most likly has several engineers working on a vehicle yard and you've only just finished your barracks. You can try catching up to your enemy by making an advanced engineer, or just go towed guns. Both options work and provide their own advantages. Soviet light vehicles are well armored and fast, while towed guns are cheap. Use the first option if you think you can apply pressure to your enemy and the second one if you think you're behind.
Fast and cheap, this is as close to a zerg as you're gonna get. You can undeploy any gun, including AA guns and late game raiding is something done almost exclusevly by soviets due to the fastest tank in the game being also one of the cheapest. Cheap infantry means a loss is not such a big deal, since more can be made really fast. Soviet weapons are known to be the most accurate ones, especially anti-tank weapons, giving a much more reliable solution to enemy armor then other factions. Soviets also possess the cheapest buildpower, at about 330 per constructor, which can also cloak to hide from enmy units and infiltrate enemy bases, possible making mines, barracks and other nasty suprises. When soviets get raided, they don't rush their AT guns to the storages - they rush the storages to the AT guns. As the faction with the only mobile storages in the game, you can never truly know where you should attack to make it hurt. And if you don't catch a soviet by suprise, the supply truck will just outrun most invaders.
While having speed and good aim helps, soviet guns are generally weaker and not as well armored as enemy equivelents. Infantry captures flags at a slower rate (about 10 times slower, meaning a squad of soviet infantry will capture flags as fast as a single rifleman). This is compensated by having commisars capture 10 times as fast as normal infantry, forcing you to constantly make a decicion: to build, or to expand. Soviets are always slower to get tanks, as they do not start with normal builders like others, but rather basic builders and making a barracks before able to do anything else really slows the soviet start. If soviets chose to be mobile, undeployed trucks are vulnerable to fighters and intercepters, as they can start attacking before entering the ranges of your AA, easily popping the ammo supply.
Using your barracks, you shuld keep in mind, that soviet infantry consists of poorly trained soldiers, who were recently givin a gun and told to face a particular direction. As a result, soviet infantry is much cheaper then the professional infantry of other factions, but weaker in most aspects. Mixing in professinal or specialized infantry will greatly boost the overall effectivness of your forces, such as maxim HMG's, mortars and snipers. Engaging in combat is usually very risky for soviets, as equal numbers of enemy troops will always defeat the soviet force if fought on even terms.
When making the towed gun yard, you may notice that the yard itself does not make any advanced constructors or artillery, like other factions. In fact, the options in the yard are pretty limited, forcing you to buy one of the upgrades to make anything useful for later stages of the game. The tank destroyer upgrade will serve you untill the very end, assuming the enemy makes any sort of armor, while mobile artillery will give you the su-76 and the rocket artillery, usefull only in some situations. The mobile artillery upgrade is used mostly for the rocket artillery, as the SU-76 can be made much cheaper by making a light vehicle yard normally. The towed gun yard is still a must have at later stages of the game, as it provides you with proper AA weapons, cheap AT guns and can help with high tier armor with the tank destroyer upgrade. Also good to note, the soviet M-30 artillery is the most powerful in the game, dealing nearly double damage per hit and capable of destroying medium tanks if hit directly. They are, unfortunatly, the shortest ranged artillery units and one of the least accurate.
When using the light vehicle yard, you should note you have several units with over lapping roles: the BA-64 and M5 halftrack for anti-infantry support, the M5 with the GAZ-AAA for anti-aircraft protection, the T-60 with the SU-76 for anti-armor and anti-infantry support. They are similar, and, in most cases, can be used interchangably. The BA is cheaper then the M5, but is slower to aim, cannot fire at air and cannot transport units, as well as not giving infantry a supply zone for fire rate bonuses. The T-60 is much better armored and less clumsy then the SU-76, but doesn't quite pack the punch with it's much smaller gun. The T-60 is much better suited for raiding, as usually 1-2 of them can destroy a storage if the enemy is not careful, while the SU-76 can destroy most vehicles at this stage with one shot, as long as nothing shoots it first. The light armor upgrade gives access to the valantine tank, a well armored, but very slow tank. It's use is debatable, but getting it is much easier then the T-70.
At the tank stage, you will encounter certain difficulties no matter what. Reasons being, that the T-34 is faster, but generally weaker then most other tanks of this level. The T-70 is excellent for infantry support, partly due to it's low cost and great front armor. Finally, the ISU-152 is something you should have around for the early anti-armor solutions, as it's relativly cheap and can destroy any tank of it's size with one shot and anything else with two. Your main focus will probably be the t-34, as soviets the enemy bottom up, rather then top down, so raiding and guerilla attacks are your main form of offence, while the ISU should help you stop enemies from accumilating too many tanks of their own. When you reach the point, when raiding is just not enough, you will probably ask: "where is my main weapon?". As a soviet, your main weapon is the T-34-85, available after upgrading your factory for advanced medium armor. Cheap (1.5 times as expencive as the 76mm T-34, just as fast, much better aarmor and a great 85mm gun, this tank should serve you well in almost any situation. While the other, heavy tank upgrade, provides you with the IS-2, which can be considered a more expencive, slightly weaker version of the ISU-152, but much better suited for long range combat, as well as a much more accurate weapon and even more armor.
When times call for air combat, the soviets win almost always. The fighter, LA-5FN, is just about the best fighter in the game, so you can be sure that as long as you have one of these in the air, you will make the enemy work very hard for every dropped bomb. The intercepter, Yak-9U, is closer to average, but still a threat to anything in the air. Like most intercepters, used when a quick reaction is needed, not a powerful one. When it comes to bombers, the soviets has the clumsy IL-2M and IL-2M PTAB, both knowing only about the basic concept of turning, so you need to give them plenty of room to make a proper bombing run. The IL-2M does wonders against buildings, light armor and even infantry with it's rockets, while the PTAB version clears whole lines of enemy armor, both light and heavy. Soviet air play is powerful and direct, with clearly defined roles for each unit, but without gimmicks or toys often found in other arsenals.