[...] though these skills currently become less useful in the endgame. However, we are in the process of changing this. All ship skills will grant some bonus to the ship above it. So an Assault Cruiser will benefit from Starship Captain, Cruiser Captain, Heavy Cruiser Captain, Exploration Cruiser Captain and Assault Cruiser Captain, but it will get the most benefit from Assault Cruiser Captain Skill. So if you want to maximize your Assault Cruiser, you will need all those skills. Note, the Assault Cruiser will not gain any benefit from the Star Cruiser Captain skill and vice-versa. The bonuses only affect ships upwards along the tree, not laterally.