Can't kill drengin Dreadnaughts

Due to the way the battle system works, both sides in a battle are not allowed to be destroyed simultaneously, so the stronger of the last ships on each side that were alive is revived with 1 HP.

The simple way to beat it is to send a fleet that won't get annihilated by it. Namely, just use a swarm of tiny ships with 1 attack; if you have more ships than the dreadnought has weapons, it won't be able to take them all out before you take it down.

I must have explained it wrong. I came in with fleets of five large hull ships with no defence and full of pyschotic lasers or whatever they are called. my total fire power was more than their ships. I would attack them on planets or in the open. The only time I could kill them was when they attacked me and didnt kill all my ships. Their HP was roughly 130, and my first two shots would take off 129 and my next three shots would take off 0,0 and 0. I would leave them with no HP, bring in another heavy hitting ship and it would take off 0. I hope that explains it better.  

Then they must have at least five weapons on their ship, each weapon capable of destroying each of your ships in one round.

Like Kryo said, you must have more ships than they have weapons, so use all tiny hulled ships fleeted with one powerful ship, that should do it.