This Circular Ship Was the Weirdest Warship Ever Built

After its defeat in the Crimean War (1853-1856), the victorious powers forbade Russia from operating battleships on the Black Sea. Once these restrictions ended, Russia rebuilt its Black Sea fleet with modern warships that it hoped could defeat the navies of France and Britain should they ever cross again.
From 1872 to 1874, Russia built on the Black Sea one of the strangest-looking warships the world had ever seen. Andrei Alexandrovich Popov, the naval officer responsible for the design, wanted an ironclad monitor, which was a common naval design concept. But Popov built one had a circular hull. The Novgorod weighed 2,490 tons and had a diameter of 101 feet. It carried 2 12-inch guns that retracted into an armored turret. The guns sat on a turntable that could move 35 degrees in either direction. The ship had 6 engines, each of which powered 1 propeller.

(The cannons of the Popov via Mehl's Naval Guns)Russia followed up on the design by building a larger version from 1874-1877. After testing the Novgorod’s seaworthiness, Popov decided that the second ship should be bigger. So the 3,550-ton Vice-Admiral Popov had a diameter of 120 feet. It was named in honor of its designer.
Popov’s ships had a rare design premise—and for good reason. They often floundered even in calm water and rivers, let alone the open sea. Worse, when idling, Novogord and Popov tended to spin in circles. The Czar, however, was fond of the design and ordered the construction of the Livadia, a circular royal yacht. Historian Stanley Sandler jokes that this must have been because the Czar “presumably suffered more from seasickness than dizziness.”

(The royal yacht Livadia via Larry Neilson)Nonetheless, both warsships performed adequately during the Russo-Turkish War (1877-1878) in which Russia bested its longtime enemy. The Novgorod and the Popov served in Russia’s naval forces on the Danube River (then a heavily militarized body of water) and were in use until 1903. They were scrapped in 1912.
You can see more photos, drawings and diagrams of these ships here.