Breakthrough

Breakthrough can be a very good tool if used in the right way. Its main drawback is against good players and in a Revolt world is that it cannot be both revolt and breakthrough, which makes it more useful for Conquest worlds.

This technology makes your LS weaker, so you'll use in your OLU cities. The purpose of this is to make the OLU hits the DLU and the LS ignores the birremes.

For example. You have 50 LS in your OLU city, then you send it against a city protected by 100 birs. The breakthrough will work in this case and you will lose less FTS, consequently less troops.
The ratio can't surpass 1LS:4birs, so you have to clean the harbour with LS nukes.

If you're a sniper, then breakthrough definetely doesn't fit in you. Because you'll send the LS nukes right before your OLU lands, saving your LS and FTS in your OLU.

To recap, Light Ships and breakthrough in OLU cities are only to safely transport your troops on the enemy shore