Warships is a free Alternity supplement that replaces much of the previously released material on starship construction and combat. It was released by Wizards of the Coast after cancelling the Alternity line.
The book contains:
A fortress ship made with the new Warships accessory from Wizards of the Coast.
The Last Warhuls stats as per the Warships Supplement.
The Warships supplement can handle more than capital ships!