Image imported from derpibooru 
Original Description:
 
As the Imperial Lunar Military’s focus moved away from Equestria and the nations immediately bordering it, the need for a large powerful Navy was made clear. While a decently sized navy had been inherited from the old Equestria, the Empress would not be satisfied until she commanded a fleet that no other nation or empire could rival, and so she ordered the construction of a super-heavy battleship so enormous that its very existence would put entire fleets to shame.
 
The order was received coldly by Lunar high command, who believed that the materials used to build such a thing would be better used in the construction of an aircraft carrier, an innovative but largely unproven concept as of then. However, Empress Nightmare Moon was adamant, and insisted that the mightiest battleship in history must either be built by the Lunar Empire or not built at all, and that the very idea of the ship sailing by an enemy’s shore would instil unspeakable dread amongst their ranks. Again, high command protested by reiterating that an aircraft carrier would do this job just as well if not better, while also stating that the fear-factor would soon wear off as naval aircraft became capable of sinking ships orders of magnitude larger. But their protests were in vain; the Empress remained unconvinced and her word was final, so construction of the ILN Tantabus began.
 
Construction took two and a half years, being the primary project of Manehattan’s many dockyards. During the construction period, high command had hoped that the Empress would see sense at some point and reorder construction to instead go towards aircraft carriers, but she remained fixated on the idea of commanding the mightiest battleship in history and more money and more resources were invested into the ship. When the ILN Tantabus had finally been launched, Nightmare Moon was ecstatic, “like a foal in a candy store” as some described it. She immediately took personal command of the ship and command a live fire drill on the spot, which necessitated that the surrounding Manehattan waters be cleared of any civilian or military vessels to avoid anybody getting hurt. Additionally, the deafening noise of the ships guns were heard across the whole metropolis, meaning the drill delayed a significant amount of economic activity in the whole city for that night.
 
Despite the enormous cost, the ship itself rarely saw ship-to-ship combat as high command would later dedicate naval resources towards developing stronger carrier battle groups, with the ILN Tantabus being relegated to remaining in port as a fleet-in-being vessel with occasional use in shore bombardment. Even then, it found most use in diversionary attacks as the might and prestige of the ship would often draw enemy attention towards it and away from wherever the real target was. Most of high command agreed that the ship did nothing to further the aim of strengthening the power of the Imperial Lunar Navy, but did everything to further the aim of pleasing their Empress.
 

 
Commission I got from LittlePolly!