In practice, it seems like the defense roll really does start at 1. There are critical hits in the game (red numbers in the combat log) that do more damage.

The red numbers are shots that kill an opposing target. It's definitely possible for defences to roll a zero.

I'd say defence is:

-Better for larger ships than smaller ships
-Better for ships that have to guard something than ones that are more mobile
-Better late game than early game, as the 'other defence', hitpoints, shrink relative to firepower
-Better when you have a technological edge

Defense is way more powerful then offense, but it has ifs, which are :

1) If you have more then half the defense then your enemy has weapons.
2) If they're optimised
3) If you're not ridiculously poor

It's only with defenses that the average craft fights enough battles to go up insanely in levels. I had a squadron of medium ships at level 104 once! they had around 120 hp (instead of 12) . (I play at painful)
That means that those ships will probably never die, even if I'm slightly behind technologically.

Yeah, I love the defenses.

Just to clarify some things, ship defenses are definitely smaller than weapons, but about twice as expensive. I took notes from a Battle of the Gods game, for both Tiny and Huge hulls the trends are the same.

Consistently up the tech lines (except early missiles, which do lots of damage), a point of offence and 1.5-2 points of defence are about the same. For example, Graviton Driver II (half way down the Mass Driver line) on a Huge hull is 13 size, 33 BC, 3 damage. Tri-Strontium Armor III (half way down the Armor line) is 11 size, 70 BC, 3 defense. Damage/BC is 3/13 = 0.231. Defense/BC is 3/11 = 0.273. Price is 11BC/damage vs 23BC/defense.

At that tech level if I were to have Advanced Miniaturization, my Huge hulls would hold 112 points of stuff. Assuming I put in 27 hull points worth of engines/sensors (don't know if that's an accurate number or not), that leaves 85 points for armament. Maxing weapons gives 6 Mass Drivers, for 18 attack. removing two mass drivers would allow me room for three pieces of armor, giving me 12 attack, 9 defense.

The important part of the defense advantage comes from the fact that it's used for each time defending. If each of these huge ships was attacked by a fleet of 5 tiny hulled ships at the same tech level, the tiny hulls (with 22 points of space and requiring 8/6 for drivers/armor) could be armed with two mass drivers, for 6 attack, and would very likely do no damage at all to the ship with armor (five 1-6 damage, less five 1-9 defense). If they got the jump on the full-attack ship, they would lose a fighter each volley, but would do (5+4+3+2+1) * [1..6] damage, which is about 15 * 3.5 = 52 damage before being defeated. If the huge ship got first strike, the fighter fleet would only do ~35 damage though. Still a lot more than 0, given a fresh Huge hull has 48 hp.

If the capital ships instead fought each other, 2 ships to a fleet, assuming base HP of 48, it goes like this:

18/0 ships attacking 12/9 ships (if defense were a range from 0..x, full attack ships I would expect to do one more point of damage):
[1..18] * 2 - [1..9] * 2 = 9.5 * 2 - 5 * 2 = 19 - 10 = ~9 damage.
[1..12] * 2 - 0 = 6.5 * 2 = ~13 damage returned.

Wow, surprising myself even, I popped into Excel, and if the full attack ships strike first, the balanced pair have one surviving ship at 34.5 hp. If the balanced ships strike first, they survive with a 3-hp ship, and a full-health ship.

Admittedly, the balanced ships are more expensive, and would lose if the attacker is not the right type (18/0 vs 12/3 does 15 damage instead of 9, advantage attackers) but a little extra defense can go a long way after you get beyond 1v1 battles.

- Mome Rath

P.S. I miss forum software with a PREVIEW button

My experince at low tech levels a fleet of 3, 2 att 1 def beats a fleet of 3 3 att 0 def everytime.  With a loss of one ship about half the time.    Offences ship will average .75 points per round per ship,  Defence Ship will average 1 point of damage per round per ship.  Based on an offensive roll of 0-3 and 0-2 verus defence rolls of 0-1 and 0-0

After reading this series of posts, It reinforced a few points that have come to mind for me after playing a few games.

1. Guns always work, defenses sometimes dont. A weapon of any type can be used to attack a ship, thus a ship is always 12/0 no matter what. This attacked ship may have defenses against that type of weapon or it will not. Defense on the other hand apply to only one type of weapon, so if your carrying missle defense and the attacker uses mass drivers, your 6/6 ship just became a 6/0 ship. the result is a lot of wasted hull space for something useless.

2. Upgrade is way too frigging expensive. If you find yourself with wasted defenses(your ships use shields and theirs use missles), after early game it is prohibitively expensive to refit existing ships with effective defenses. so if your not sitting ona huge pile of cash, your fleet is at a distinct disadvantage until new types get built. An addtion to that is your new builds(while having effective D) will have no experience whereas your opponents will have at least some exp, because theyv been kicking the snot out of your ships.

Solution and work around? Using several diffent types of ships in a fleet. But with all the possible gun/defense combos available thats no guarantee. With the hull size restrictions, it is simply not possible to mount an effective defense against all types( a severe wrankle wiht me but thats for another post).

I just want to point out that while everyone here is arguing about the optimal solution, you're only underscoring an important part of the greatness of this game: Depending on the strategy you choose, different ship types are useful. Depending on the circumstances, different ship types are useful. Don't just compare stats, because stats don't take tactics into account. Try a game and focus on another type, and watch your strategy evolve to take advantage of what you're trying. It's a credit to the designers/devs that such variations can be equally effective.

BTW- Two defense examples:
1 - In a small game, I waited for an opponent to attack, and then quickly built ships that defended against his favored weapon (1/0/0 att vs 1/0/0 def). As was postulated by someone, my ships never got damaged. I know, this contradicts what someone else said, so I offer two possible explanations: a) This was pre-1.0X, and I made sure I defended against the right type of weapon. Anyway, once the bad guys discovered how to put more than one gun on, I had to change my tactics a little, but that just gave me an excuse to play in the shipyard for a while. Yay!

2 - In a big game, they've been coming after me with 6-7 attack in either beams or missiles, and I've been defending with 4/4/0 ships (note that this is equivalent to having 6 def in their chosen attack mode: either way it's 4+sqrt(4)). One on one they beat me stupid, but in equal-sized fleets I crush them like bugs (although if I have new ships I'll usually lose one).

Cheers!

if your carrying missle defense and the attacker uses mass drivers, your 6/6 ship just became a 6/0 ship

In this case, the 6/6 ship would be 6/2, since off-target defence counts according to square root. Instead, of a 6/6 ship, I might be temped to build a 6/4-1-1 ship, so it would have 6 defence against on-type attacks, and 4 defence against off-type attacks. Generally for defences, I like to stop at square numbers if I can.

I think it's important to clarify that having one point of defense on a ship will always yield a reduction in damage by one, regardless of the defense type. Sub-optimal defense types operate at the square root of their value. The square root of one is one, so having that single point in any defense type might be a good investment even if you choose a primarily offensive strategy. Maybe just research into that one defense type until it's as compact as it can be.

As far as I can tell, red numbers don't indicate critical hits. Those are hits that caused a ship to be destroyed. However, I do think there are critical hits. No idea what percentage chance or anything. It stands to reason that there must be, since a 1/1 vs a 1/1 will actually end at some point assuming the manual is correct about damage and defense being 1-n, of course. I have seen ships hit for more damage than their attack rating, so that would indicate the presence of critical hits. I haven't seen it often however.

I think my worst fight ever was when I sent 4 ships with 10 missile attack and no defense against 2 ships with 1 laser and 22 armor...same size ships. I really wish I had 1 shield.... really. I barely scratched them despite their defense being an off type. I don't have a calculator handy to get the square root, but it's about 4.7. Most of my hits were 0 with rare 1s and perhaps a single 2. All of theirs were 1 with a rare 2. I lost bad.

i havent played enough to get a final conclusion on the defense issue, but i completely agree with amanasleep on this one:

I sometimes find amanasleep "trolling" and harsh, but often I agree too. Amazingly, incomprehensibly, MOO1 really is still the gold standard for 4x tech trees. And I don't like the GC2 tech tree, it's too generic... 75% of the advancements have no obvious effects, or give you a starbase module that gives no obvious effects. When I got a new tech in MOO1, it was always really exciting and something I would immediately use. A new tech in GC2 is like... huh, Lasers 3, now I can fit an extra laser on my small ships... oops, no, still can't. Guess nothing changed.

Ever play Space Empires IV? I think it has an awesome tech tree and the combat system is a straightforward d100 with pluses for certain offensive components (combat sensors, crew experience, etc) and minuses for defensive components (ECM modules, crew experience, small ship size, etc). It's economic system is also much cleaner and realistic (although you still can't do everything due to prohibitive expense). Good online community and PBW service as well..........Sorry EA, you can take some lessons here.......Nevertheless, there are some features that I like about GalCiv so maybe it's all a wash. In the end, the gaming community wins

All of this shows a lack of imagination on the developers' part, as tried and tested theories of combat modeling were thrown out in favor of a rock paper scissors system that doesn't work and furthermore consumes most of the tech tree pointlessly. I have said elsewhere, and will say again, the MOO1 tech tree is the gold standard for such things, encompassing many different strategies for gaining dominance without getting bogged down in "replace +1 widget with smaller +1 widget or with 50% larger +2 widget." GC2 techs are all incredibly generic and not fun to research or achieve. Taking out tactical combat considerations is the likely culprit here, as weapon range, tactical ship speed, and area effect weapons, stun effects, cloaking tech (although that one could be used strategically too - where's the cloak, Stardock?), and a host of other fun sci-fi elements are absent, and no fun gameplay replaces them.

I agree on this one too