You can build your warship faster if you have the colonies already producing either colony ships or constructors. You can either design or just pick a core ship. Once you have saved the ship go to the colonies table and make sure every one is doing the same build. Once that is done go to the govenor and change the build to the warship. Make sure that you use the military slider to lessen the time it takes to build the warship. In about 11 weeks at max you will have a really big jump in you military strength. I only colonize large planets so that I can have at least three factories on each of them. By the time the enemy comes each planet will have a guardian force already for them.
