I played a game against the ai on veteran difficulty (minus the experience bonus) where I declared war on the USA on turn 1 in 1914.
Unfortunately, other than sporting some impressive tech (infantry weapons level 2 way before anyone else), the USA did very little. I spotted a USA corps in France as early as 1915, but they made very little difference as France was already clogged with Entente units (+20% MPP and various AI bonuses). Some American DD eventually did attempt some ASW near Germany (I didn't do any atlantic sub raiding in this game). That was about it for the USA. Russia surrendered and the Entente lines are broken in France and Italy.
The AI is not bad for an AI, but it just can't compete with the human brain. It's especially bad once the front breaks down in either a major or minor way. For example if you obliterate one row of their line too quickly, they often rush or rail in replacements to "fill the line" in France, often neglecting to entrench. The AI doesn't seem to consider when falling back may be the best option (for example if I have four artillery pieces aiming at a certain area, it's probably better to not attempt to move units in even if they do entrench). And even worse is the Russia AI which has no concept of how to continue the war once one of their fronts gets busted open. They usually send 1-3 units to each town and just sit there, slowly getting encircled. Their HQ seem confused about where to be, often clustering uselessly in the Ukraine without an army, or sending too many rebuilt corps to the Caucasus where nothing is happening. The AI doesn't understand how to maximize artillery usage which is a big deal. Probably half a dozen times at least where the AI correctly fired many artillery shells at one of my units and then either didn't follow up with an attack or only followed up with a halfhearted attack that failed to destroy my unit.
Tech wise the AI makes some strange choices. It's not prioritizing Industrial Tech enough. That technology is overpowered (should be nerfed to +10% instead of +15) and a must have, but looking at the MPP graph I don't think the UK or Russia researched it. France seems to have researched Industry. The AI got Infantry Weapons EXTREMELY quickly. Russia was sporting them in mid 1915 when Germany was only 49% done! This was probably the result of a few lucky research breakthroughs (too random in my opinion, should be reduced in effect). They are also fairly quick to get artillery tech, but don't quite prioritize artillery and shell production enough, as they lagged slightly behind getting artillery weapons 2 and the highest shell production techs (both overpowered techs). In some ways the AI actually outpaced me in tech, as they were sporting high levels of ASW when I hadn't researched any ASW or sub tech yet.
The naval AI needs to understand that it's too dangerous to hang out near enemy ports. Especially once I get blimps and subs for spotting. It's attempting to do ASW missions near my ports that harbor BB and DN. Although I didn't consciously attempt this, I believe it's possible to bait the ai into sending a group of DD/CL near your ports/fleet by simply having subs near your ports.
Their NM was actually quite high throughout most of the game (UK is still sitting at 97% and the USA is at 114%). I think the AI gets some bonus where it gets free NM every turn. Also the USA joining in the beginning gave them all a boost. At one point I was rapidly destroying French corps and their NM was actually rising. However once you take Verdun and Warsaw I believe France and Russia start getting ticked in NM every turn. Eventually Russia collapsed, but only after I had conquered pretty much every NM objective available besides Petrograd and Moscow.
It's March 1917 and losses counts of all types except naval mines and partisans are