I attack it in fleets of 4-5 ships (mixed medium and large hulls). Collective 130 offensive points, 0 defensive. The dreadnought has 1300+ attack, 0 defense and 113 initial hit point. It took me 2 fleets to get it down to 1 hit point but then as I threw more and more fleets at it with same stats (5 fleets at least) it just keeps crushing them while remaining with 1 hit point. Doesn't make sense.
BTW: I can destroy weaker dread lord frigates (23-28 hp) without problems usually with a single fleet.
Thx,
-Ed