BearMan
One More Turn...
1. Preface.
2. Modern unit reference.
3. Tanks & infantry without artillery or airpower support.
4. Carrier group attacking a city.
5. Armor with artillery & stealthbomber support.
6. Armor with artillery support invading Moscow.
1. Preface
Below follows a few battles that I belive covers most of the modern warfare. These are balanced battles, non balanced warfare isn't interesting (if you use your units right

2. Modern unit reference
Ground Units
- Modern Armor 40/2, first strike, Blitz.
- Tank 28/2, Blitz.
- Infantry 20/1, +25% vs. gunpowder.
- Mech Infantry 32/2, 20% aircraft intercept.
- Marine 24/1, +50% vs.machine gun and artillery.
- Machine gun 18/1, +50% vs. gunpowder, first strike, NDB.
- SAM infantry 18/2, Range 1, 40% aircraft intercept, +50% vs helicopter.
- Artillery 18/1, withdrawal 25%, collateral, +50% vs siege, bombard -25%, NDB.
- Spy 0/2, 4 allowed, invisible to all units, Primary mission is to defend/attack oil, uranium, aluminium and spaceship production.
Other units you might encounter ....
- Navy SEAL 24/1, 1-2 First Strikes, +50% vs Machine Gun and Artillery, Amphibious, March.
- ICBM 0/1.
- Panzer 28/2, Blitz, +50% vs. Armor, NDB.
Air Units
- Gunship 20/4, withdrawal 25%, +100% vs Armor, NDB.
- Fighter 12/1, range 6, 50% intercept, bombard -5%.
- JetFighter 24/1, range 10, 70% intercept, bombard -10%.
- Bomber 16/1, range 8, -50% vs naval, collateral, bombard -15%.
- StealthBomber 20/1, range 12, collateral, -50% vs. naval, 50% evade intercept, bombard -20%.
Naval Units
- Destoyer 30/8, Can see subs, Intercept 30%, bombard -15%.
- Battleship 40/6, Collateral, bombard -20%.
- Submarine 24/6, withdrawal 50%, Cargo 1.
- Transport 16/5, Cargo 4.
- Carrier 16/5, Cargo 3.
3. Tanks & infantry without artillery or airpower support.
City attack.
6 Tanks trained for city attack.
4 Tanks trained for collateral damage.
2 Marines.
4 Infantry.
City defence.
6 Infantry trained for city defence.
1 Machine gun.
Outcome
The collateral damage caused by the the tanks is not enough, the attacker will take the city, losing almost every unit in the process.
Conclusion
It is not possible to take a city in the early modern times without Artillery or Flight, trying will bring the invasion to a halt. The priority for early modern combat research is Flight, it brings the priceless bombardment without losses (known from civ3

I belive priority training for artillery is collateral damage:
Barrage I (+20% collateral damage) makes the next artillery unit to attack have much higher survivial chance, since they get a change to actually kill an enemy, because of the damage allready done by the first artillery attack.
Priority in offensive military research is the collateral damage units, they are much more valuable then Tanks.
Let me correct that, Priority in ANY military research is the collateral damage units, otherwise you will face the infamous SoD (civ4 style = combined arms

You can invade with Infantry/Flight or Artillery/Infantry,
you can NOT invade with Tanks/Infantry!
Best is to have them all:
A few airstrikes followed by artillery fire and then just send in the tanks and infantry

Final conclusion
Use standard military tactics, and your losses will be minimal!

use CIV3 tactics, and you are doomed !

A side note
I like the civ4 way of combat, it is much more realistic, I am even getting along with the "must attack with artillery feature", In my mind, I think of it as that the unit that comes under artillery fire, directly attacks the artillery, therefore, the artillery gets killed by mortar fire, by Humvee flanking attacks, or another infantry division that is called in to flank it.
4. Carrier group attacking a city.
City Attack
2 Carriers
6 Jetfighters
3 submarines.
2 battleships.
(And 2 Mech Infantry, 2 Marines, and 1 SAM infantry on the ground outside the city).
City Defence
1-3 Fighters and SAM infantry.
(Alot of ground defence (>10 Units)).
Outcome
While the Jetfighters survive their strike missions, they don't manage to inflict much damage. They get intercepted often and spend alot of time on the carrier repairing. They couldn't Inflict any significant damage on the ground defence in the the city. The submarines took a few hits from airstrikes, notting they couldn't repair in a turn or two, Jetfighters on intercept mission shoot down 1 bomber and 2 fighters.
Conclusion
Carrier with jetfighters is only useful for strike against non AA targets, they do a fine job intercepting any bombers against the carrier group thoe.
Final Conclusion
The Carriergroup couldn't reduce the city defences enough for me to attack with the ground force.
Peace followed.
5. Armor with artillery & stealthbomber support.
Attack against a country
5 Modern Armor.
2 Artillery.
5 StealthBombers.
1 Spy (was scouting there long before the war started).
Defence of 4-5 Cities (per city)
4-5 infantry in each city.
0-2 Destoyers in harbor.
0-2 Cannons.
0-1 Tanks.
Outcome
2 airstrikes (2x5) against each city takes down every defender to half the strength (from ~20 to 10), The destoyers damage 1 or 2 aircrafts. The enemy cannons did some collateral damage to my stack when it reached a city, dying in the attack. Then my artillery was sent in, and after that my armor. No losses, I belive I left one armor out of the attack because it was to damaged. Roughly the same for the rest of the cities. Interesting is that even thoe the artillery had bad odds while attacking, they always survived.
(Note : After each city was conquered I left my ground units to heal 1-2 turns, while the next city was beeing prepared with airstrikes)
Conclusion
Having airsuperiority (with bombers!) does it, I could as well have attacked with infantry and normal bombers, the outcome would have been roughly the same.
Final conclusion
if your enemy have invented Flight and he is within bomber range of you (carriers can't carry bombers) and you do not have either fighters (flight) or SAM infantry (Rocketry)
-> Diplomacy or Surrender is your options

If the situation is the reverse, you just bought yourself a new country for the price of only losing 0-2 units, if you bother to send in a few infantry units or tanks, that is

Side note
I was 2 supieror in this last game, (each battle is from a different game) increase from Prince to Monarch difficulty is needed (or not as good starting position as last time (I had both iron and copper, and manage to settle 3 cities, small map, high sea level, continents, 18 civs). My early expansion was made with 8 praetorians, 2 catapults, 4 axemen and 4 spearmen, with this I took out 3 countries, they had 1-2 cities each.
6. Armor with artillery support invading Moscow.
Attack
2 Modern Armor.
2 Marines.
3 Artillery.
1 SAM infantry.
Defence
6 Infantry.
4 Fighters.
2 Artillery.
Outcome
The attacking artillery lowered the defence of Moscow from +60% to 0% in one turn. The artillery in the city attacked and did limited collateral damage. The next turn the Armor killed 4 infantry units. Then the Artillery attacked killing one infantry, then the Marines finnished of the remaining defence artillery. The SAM infantry damaged one fighter, 20%.
Conclusion
Gunships/Modern armor are the only units that destroys a modern armor assault.
Final Conclusion
Modern Armor always works wonders with infantry

Side Note
I find Monarch level to be fun and balanced, Russia was not my largest enemy (8th country or something). I got attacked by the 4th largest country and he sent 5 destroyers and 3 transports. I barely made it, having only 2 destoyers and 1 battleship. I could attack a few of the destoyers directly after he made landfall, because his fleet split up to pillage my sea improvements, but I had to stay away from his main fleet or I would have lost all my ships in the initial attack. I only regained control of the Sea by building new battleships, took 10 turns or so. Then work boats to repair all my improvements. On land I gathered 2 artillery, 2 marines, and 2 Infantry to defend the city where the stack made landfall. The stack took 3-4 turns to kill. In the end I won a spacerace victory in 1915 AD.