My post seems to have disappeared, odd.
The key problem with Machine Guns that after Steam Power, you have the choice of going for Assembly Line or Railroads...usually you'll go for Assembly Line, since it gives factories, infantry, and allows you to begin the Pentagon. After researching Assembly Line the next twenty turns or so for me are tied up building factories and power plants, and by the time they're done I've researched Combustion and Industrialization, and start building tanks. I just don't have the oppertunity around that time period to devote to building new defensive units.
They also can't upgrade to Mech infantry later on down the line, so any production put into them sort of ends up being wasted, unless you upgrade them to SAM infantry, my next topic.
I think the problem with SAM infantry right now is due to a chain of causes. SAM infantry's main purpose is to counter lots of gunships, but the AI almost never builds gunships unless you build a ton of tanks. They never build them because gunships' main purpose (other than killing tanks) is pillaging behind enemy lines, and currently the AI has no scripts relating directly to pillaging.
They'll pillage on the way to a city, and if the attack force has bad enough odds; they'll attack a pillaging force if it poses a threat to their cities, but other than that there are no direct "pillage" or "counter-pillage" scripts in the AI routine. I think when the pillaging gets coded we'll see a lot more use of gunships, improving the value of SAM infantry, and thus the value of machine gunners. Nonetheless, allowing machine guns to upgrade to mech infantry would still be very beneficial for guns built for city defense.
I think Ironclads could be the perfect intermediate stage between wooden ships and modern destroyers if properly reworked. They could possibly be replaced with a Dreadnought class ship, a WWI - era vessel to bridge the gap between sails and steel.
Subs just aren't powerful enough. I've found that anything I can do with subs in combat, I can do better with an equivilant number of hammers of carriers + destroyers. Figher-laden carriers can also be used to bombard improvements, strafe troops, intercept enemy fighters, and can be rebased instantly; they also die even less frequently than subs do. Usually I only build one or two subs, to transport spies.
Explorers are
very useful. You get them a tech before Caravels, so you can have a few built and ready when your ships pop out and accompany them around the world to drop off on new continents and chart other leaders' territory. Explorers are also my ideal medics, since they are very cheap and move 2 squares regardless of terrain. They also have 4 strength and +20% defense in hills, forests, or jungles, so they hold up pretty well against barbarians or when the last man standing in a stack. They're classified as recon, so nothing gets combat bonuses against them.
Marines have a higher base strength than Infantry, but are also proportionatly more expensive. So they're more powerful, but cost more...and usually for behind-the-front-line city garrisions it's just as effective to have two infantry as two marines. I re-station tanks or aircraft in the area if there's enemy forces nearby, so it's mostly just need to have
some unit in the city, and Infantry cost less. Whenever there's a river near a city I just maneuver around it so the entire army can attack without a penalty. On the other hand, if Machine Guns became more useful, Marines would as well.
Pikemen are useful. I always bring a few along to keep the AI from building too many mounted units. They're not good on the offensive though, since macemen or crossbowmen are likely to defend in a stack.
