My Light Gunship design

I have Combat Sensors standard on many ships, especially the bigger ones and on bases.
Even at lvl 1, that extra 5% bonus to hit can be useful, especially on bigger ships with many guns, and for PD and other weapons against units, where every little bit helps.

It might be better at first to go with an extra gun, but after you start getting better sensor tech (say at least lvl 10), then having three guns with much better accuracy is likely better than 4 guns with no added accuracy, especially in terms of damage done vs. ordnance used.

Upon getting further into sensor tech, when Combat Sensors become even more effective, then there is usually no reason to not put one on a ship unless there is actually no space for it. IIRC, at max level, they give something like a 65% bonus to hit.

Once I get a little ways into the right techs, I will usually prefer to have Combat Sensors and ECM rather than adding an extra gun, as being more accurate and harder to hit is more useful in a longer battle, because extra firepower doesn't work to well if you can hit as much and if you get taken out earlier in the fight.

If the enemy uses ECM, Fighters and/or Drones, that is another reason to use Combat Sensors.

For now, I would have to say you should stick with 4 DUCs, you can probably get away with not using Combat Sensors until you get combat Sensors to about lvl 10-12, then the accuracy bonus will be enough to compensate for removing a gun without having any real effect on overall ability to dish out damage. The other 20kt freed up could then be used for ECM to improve survability, and perhaps also an extra armor or two, to help them stay in battle longer.

On a side note, my 'gun ships' usually use Meson Blasters, they are smaller than DUCs, and use no ordnance, so you can fit 50% more of them on a ship and use any ordnance storage for other things.

You could put 6 Meson Blasters in place of 4 DUCs, and be able to use ordnance storage for other stuff, either supply storage or armor, or go with 5 Meson Blasters, a Combat Sensor and an ECM in place of 4 DUCs, and any ordnance storage can be swapped for supply storage or armor.

It of course depends on your design and strategies, but IMHO, a combat sensor, even lvl 1, is mandatory for any ship with more than 50kT of guns. It can tremendously improve your combat efficiency.

Imo it highly depends on chances to hit (target, weapon, distance), so ship with APB does not need sensors as much as one with DU or MB.

If your chance is 95%, 5% gives you only 1/19 more damage
if your chance is 10%, 5% gives you 1/2 more damage

Exactly!