Slitherine

I'm not sure how surrenders work . Does the unit have to be fully suppressed, then it takes damage and can't retreat because of ZOC? Also I don't understand how this gains you prestige.

a) a unit surrenders if it cannot retreat (either because it's fully surrounded or it can't cross a river, mountain)
b) AFAIK, since patch 1.20 you get prestige if you force a surrender (equiv. to unit destruction)

So, what's not to understand?

Stmcla wrote: Also I don't understand how this gains you prestige.

Think of prestige as fancy points. You got fancy and enveloped and surrendered the enemy thus avoiding a costly and bloody inhumane struggle. High command then uses your victory for propaganda value making of you the Second Coming. Next time you ask for a King Tiger they probably will not dare say no, you being Mr. Fancy pants and all.

In game terms this is abstracted as awarding you prestige points.

All entrenchment must be destroyed before a unit can retreat.

I can't recall if it has to be fully suppressed.

No, it doesn't have to be fully suppressed, but the total suppression from the already existing and resulting from the attack must be equal to the remaining strength.

So the conditions for an unit to surrender are the following:
- its entrenchment at the moment of surrendering must be 0 (which mean it must be 1 or 0 at the moment it is attacked, as every attack reduce entrenchment by 1)
- the suppression points at the moment of surrendering must equal the remaining strength (the persistent suppression from bombing plus the suppression caused by the attacking unit at the moment of surrendering)
- cannot retreat to another location for any reason (all hexes around occupied, out of fuel, impassable terrain)

actually i found out of fuel does NOT prevent retreat.

Indeed, since retreat is not regarded as travel.
A few days ago, there was a thread about this topic...

Surrender prestige is related to remaining strength points relative to the original strength. 10/10 you get prestige related to the base cost, 12/10 you'd get 20% extra, and 8/10 you'd get 20% less. As far as I can tell from watching how much prestige I get from surrenders, it is the strength AFTER the final attack that matters, not the strength before. If anyone can confirm this, please do.

Some units have a base strength of 1 (so that they can't be reinforced). If you can force surrender when they are quite strong you can get a huge prestige bonus. I caught a Churchill in AK that was something like 7/1 or 8/1 strength at the time it surrendered and I got about 1400 prestige. I really needed it at the time, so it was much appreciated.