Since you start the game with level 1 ships, those ships have the Level 1 power starting from the beginning of the game. When you gain reinforcements, those ships have powers too. Level 1 ships have level 1 powers. Level 2 ships (when gained) have Level 2 powers, & level 3 ships (when gained) have Level 3 powers.
So, the level 1 ships only get the level 1 powers, level 2 only gets the level 2 powers and can't use the level 1 etc?