From frood.net calculator:

Average outcome of 10,000 battles

**Attacker: 3 Inf. v. Defender: 1 Inf.**

Average battle duration: 2.5 rounds of combat

–------------------------------------------------------------------------------

Overall %*: **A. survives: 89.3% D. survives: 8.6% No one survives: 2.1%**

Average outcome of 10,000 battles

**Attacker: 3 Inf. v. Defender: 1 Arm.**

Average battle duration: 2.4 rounds of combat

–------------------------------------------------------------------------------

Overall %*: **A. survives: 80.8% D. survives: 16.1% No one survives: 3.1%**

Average outcome of 10,000 battles

**Attacker: 2 Inf, 1 Art. v. Defender: 1 Inf.**

Average battle duration: 1.6 rounds of combat

–------------------------------------------------------------------------------

Overall %*: **A. survives: 97.8% D. survives: 1.5% No one survives: 0.7%**

Average outcome of 10,000 battles

**Attacker: 2 Inf, 1 Art. v. Defender: 1 Arm.**

Average battle duration: 1.6 rounds of combat

–------------------------------------------------------------------------------

Overall %*: **A. survives: 95% D. survives: 3.3% No one survives: 1.8%**

Average outcome of 10,000 battles

**Attacker: 2 Inf, 1 Arm. v. Defender: 1 Inf.**

Average battle duration: 1.6 rounds of combat

–------------------------------------------------------------------------------

Overall %*: **A. survives: 98.7% D. survives: 0.7% No one survives: 0.6%**

Average outcome of 10,000 battles

**Attacker: 2 Inf, 1 Arm. v. Defender: 1 Arm.**

Average battle duration: 1.5 rounds of combat

–------------------------------------------------------------------------------

Overall %*: **A. survives: 96.1% D. survives: 2% No one survives: 2%**

Average outcome of 10,000 battles

**Attacker: 4 Inf. v. Defender: 1 Inf.**

Average battle duration: 2.1 rounds of combat

–------------------------------------------------------------------------------

Overall %*: **A. survives: 97.6% D. survives: 2.1% No one survives: 0.3%**

Average outcome of 10,000 battles

**Attacker: 4 Inf. v. Defender: 1 Arm.**

Average battle duration: 2.1 rounds of combat

–------------------------------------------------------------------------------

Overall %*: **A. survives: 94.2% D. survives: 4.9% No one survives: 0.9%**

As you can see from this, there is very little difference between the statistical results of attacks with 2 inf, 1 art (3 units with 1 upgraded to an art for 1 extra IPC) versus 2 inf, 1 arm (3 units with 1 upgraded to a tank for 2 IPCs) versus 4 whole inf (3 units plus an extra 3 IPC unit). Since inf/art combos are about as effective statistically as inf/arm combos, I try to have 1 art per territory that I will be trading with Germany next round with Russia. The tank combo only had about 1% over the 4 inf or 2 inf, 1 art combos (98.7% over 97.6% and 97.8% respectively). You’ll also notice that making the defending unit a tank instead of an inf/art doesn’t change the win/loss percentages by that much (about 3%).

So mathematically in essence you are spending 1 extra IPC over infantry for 2 extra units of punch (1 extra attack for the artillery and 1 bonus attack to an infantry) with artillery, whereas with tanks you are spending 2 extra IPC for 3 extra units of punch (2 attack and 1 defense on the tank). Now because Russia typically has no use for the extra movement value of tanks (at least in trading territories with the Germans), buying extra punch at a 2:1 punch to IPC ratio rather than a 3:2 ratio makes better economic sense, especially considering that you are most likely going to be losing the surviving pieces when the Germans attack again anyway.

So for Russia (and usually Germany also) I usually divide my IPCs to spend by 3 to get the maximum number of units I can produce, then I look at what I have left over. If I have a remainder of 1 IPC, I’ll upgrade 1 of my infantry to an artillery. If I have 2 IPCs left over, I can either upgrade 1 of my infantry to a tank, or upgrade 2 of my infantry to artillery. If I already have enough artillery for the territories I will need to take back from Germany the next round, I will get the tank, since overall (counting the movement which can help if you need to defend extra Russian territories) tanks are a better purchase (6 total punch value plus 2 movement points for only 5 IPCs). However, I have found that for trading territories, artillery are a better purchase, since it allows you to **extend that extra attacking power into 2 territories** for the extra 2 IPCs instead of only 1 if you had purchased a tank; so I will often buy 2 artillery instead.

So let other people make fun of you for buying artillery, just play it right and you can have the satisfaction of wiping their smug smiles off their faces.