The Capital Ships and Extra Ship Slot DLC packages have been removed from the store and are now granted free, in-game at the DLC menu.
Visit the in-game "Captains Status" menu (Hotkey "H" or click the bar at the top of the screen), and select the "DLC" tab to claim it.
Posted by the game’s developer or publisher to its Steam community hub and published by Valve through Steam’s public news API. Sifter reproduces it unedited and writes none of it.