Well that depends on the settings of the ESSD doesn't it? If you want to be true to various SW sources, i'd say 10, as long as none of them get in it's forward arc. However, if you're playing Rebellion with no changes to the Bulwarks capabilities and price, i'd say you want to set it so that a squad of 6 Bulkwarks can take out an ESSD, so you need to adjust the settings on the ESSD. But. If you still want it to be realistic, if its six againist one, you should be looking to lose probably four of your Bulwarks. Remembers, and ESSD is supposed to be able to ram other ships because it's shields are so strong. It's really down to personal preference.