A screenshot of an Uncertified 'Indomitable' First Rate Deed.
Certain ships can only be built with the express permission of the Crown. In order to command this ship, take this uncertified deed, along with the correct Writ, to your national Capital to have your deed certified.
It requires 100 Royal Commendations to get the Writ for the 'Indomitable' First Rate. Or get in from Treasure Aisle (TA) for 1150 Burning Sea Points (BSP).