The siege of Port Arthur commenced in April 1904. Japanese troops tried numerous frontal assaults on the fortified hilltops overlooking the harbour, which were defeated with Japanese casualties in the thousands. With the aid of several batteries of 11-inch (280 mm) howitzers, the Japanese were eventually able to capture the key hilltop bastion in December 1904. With a spotter at the end of a phone line located at this vantage point, the long-range artillery was able to shell the Russian fleet, which was unable to retaliate against the land-based artillery invisible over the other side of hilltop, and was unable or unwilling to sail out against the blockading fleet. Four Russian battleships and two cruisers were sunk in succession, with the fifth and last battleship being forced to scuttle a few weeks later. Thus, all capital ships of the Russian fleet in the Pacific were sunk. This is probably the only example in military history when such a scale of devastation was achieved by land-based artillery against major warships.