The Russians quickly learned, and soon employed, the Japanese tactic of offensive minelaying. On 15 May 1904, two Japanese battleships, the and the , were lured into a recently laid Russian minefield off Port Arthur, each striking at least two mines. The "Hatsuse" sank within minutes, taking 450 sailors with her, while the "Yashima" sank while under tow towards Korea for repairs. On 23 June 1904, a breakout attempt by the Russian squadron, now under the command of Admiral Wilgelm Vitgeft, failed. By the end of the month, Japanese artillery were firing shells into the harbour.