Below are a series of images designed to amuse beyond comprehension. :D

I worldbuildered a Spearman with all available promotions:
Combat Line, Medic Line, Drill Line (is that possible? I added them, but wasn't sure), Woodsman Line, Guerilla Line, City Raider Line, Blitz, Ambush, Cover, Shock, Amphibious, Commando and all Great General promotions.

Then, I added a Barbarian Tank, and let the Spearman attack. Basically, if you want a Tank-beating Spearman, give it all it can get! (That's the tip :p )

http://i241.photobucket.com/albums/ff136/kamikazeshadow/Civ4ScreenShot0086.jpg
http://i241.photobucket.com/albums/ff136/kamikazeshadow/Civ4ScreenShot0087.jpg
http://i241.photobucket.com/albums/ff136/kamikazeshadow/Civ4ScreenShot0088.jpg

I bet an unpromoted spearman would have won too :). What difficulty were you playing at?

you should post the game log showing combat strengths and hits of each unit

Very hard to believe, although I am not doubting you.

With all promotion attaching a tank

4 base
+100%

which is 8 for the spear versus 28 for the tank. Must have been 8 first strikes and each landed and did good damage.

I think the point is that up to a certain level you get few "free" wins vs. barbarians. So it doesn't really matter what unit he was using he would win anyway. The real odds would be indeed very low.

http://i243.photobucket.com/albums/ff31/semirami/Civ4ScreenShot0000.jpg

http://i243.photobucket.com/albums/ff31/semirami/Civ4ScreenShot0001.jpg

http://i243.photobucket.com/albums/ff31/semirami/Civ4ScreenShot0002.jpg

The difficulty level is deity.

Dag. I was playing on Prince...
The retreat odds were 70.8%, and the combat odds were around 8%. I don't have the save, since I opened the game for this purpose only.

I've never tried that lol
go tank!

:spear:

Control +W and you can have your own play-it-yourself spear + tank battle ...

Add a forest for the tank's square. Should gain you an additional 2 strength from Woodsman III (If my math is right).

On prince one or two win against barbs are free, so you need to slaughter some barbs to get tohse out of the way.

Also i would concider letting the spear defend. This way he can get more out of those Terrain Promotions... Plant him on a forsted hill... Best across the river too... and of course 5 turns fortified... Perhaps if you stack up enought stuff he have a realistic chance of winning...

<UnitInfo>
<Class>UNITCLASS_TANK</Class>
<Type>UNIT_TANK</Type>
<UniqueNames>Spearman Killer</UniqueNames>
<Special>NONE</Special>
<Capture>NONE</Capture>
<Combat>UNITCOMBAT_ARMOR</Combat>
<Domain>DOMAIN_LAND</Domain>
<DefaultUnitAI>UNITAI_ATTACK</DefaultUnitAI>
<Invisible>NONE</Invisible>
<SeeInvisible>NONE</SeeInvisible>
<Description>TXT_KEY_UNIT_TANK</Description>
<Civilopedia>TXT_KEY_UNIT_TANK_PEDIA</Civilopedia>
<bMechanized>1</bMechanized>
<UnitClassUpgrades>
<UnitClassUpgrade>
<UnitClassUpgradeType>UNITCLASS_MODERN_ARMOR</UnitClassUpgradeType>
<bUnitClassUpgrade>1</bUnitClassUpgrade>
</UnitClassUpgrade>
</UnitClassUpgrades>
<UnitAIs>
<UnitAI>
<UnitAIType>UNITAI_ATTACK</UnitAIType>
<bUnitAI>1</bUnitAI>
</UnitAI>
<UnitAI>
<UnitAIType>UNITAI_ATTACK_CITY</UnitAIType>
<bUnitAI>1</bUnitAI>
</UnitAI>
<UnitAI>
<UnitAIType>UNITAI_PILLAGE</UnitAIType>
<bUnitAI>1</bUnitAI>
</UnitAI>
<UnitAI>

<UnitAIType>UNITAI_COUNTER_SPEARMAN</UnitAIType>
<bUnitAI>1<bUnitAI>

</UnitAIs>

That should fix it.