Vice Admiral Stepan Makarov (1849–1904) took command of the First Russian Pacific Squadron with the intention of making plans to break out of the Port Arthur blockade. By then, both sides began a policy of tactical offensive mine-laying by laying mines in each other's ports. This was the first time in warfare that mines were used for offensive purposes. In the past, mines were used as purely defensive purposes by keeping harbors safe from invading warships. The Japanese mine-laying policy was effective at restricting the Russian movement of its ships outside Port Arthur when on 12 April 1904, two Russian battleships; the flagship, , and ran into a Japanese minefield off Port Arthur with both striking mines. Petropavlovsk sank within an hour, while Pobeda had to be towed back to Port Arthur for extensive repairs. Makarov died on Petropavlovsk. However, the Russians soon learned the Japanese tactic of offensive minelaying and decided to play the strategy too. On 15 May, two Japanese battleships — and , were both lured into a recently laid Russian minefield off Port Arthur, both striking at least two mines. Hatsuse sank within minutes taking 450 sailors with her, while Yashima sank under tow a few hours later. The Russian fleet attempted to break out from Port Arthur and proceed to Vladivostok, but they were intercepted and dispersed at the Battle of the Yellow Sea. The remnant of the Russian fleet remained in Port Arthur, where the ships were slowly sunk by the artillery of the besieging army. Attempts to relieve the city by land also failed, and after the Battle of Liaoyang in late August, the Russians retreated to Mukden (Shenyang). Port Arthur finally fell on 2 January 1905, after a series of brutal, high-casualty assaults. Russian submarines By 25 June, the Imperial Russian Navy had secretly purchased its first naval submarine, known as Madam, from Isaac Rice's Electric Boat Company. This submarine was originally built under the direction of Arthur Leopold Busch as the American torpedo boat Fulton. It was a prototype of the Holland Type 7 Design known as the Adder-class/ submarines. By 10 October, this first Russian submarine was officially commissioned into service and shipped to the eastern coast near Vladivostok Russia and was renamed Som ("Catfish"). This first Russian submarine was not ready in time for the Russo-Japanese War. The reason behind this delay was partly due to a late shipment