he secured the decisive supremacy of the sea in the Gulf of Pechili, and rendered possible at last the important movements on land which the strategists at Tokio were waiting to initiate. [Sidenote: Captain Oda and His Mines] The arrangements of the Japanese were carried out with their usual thoroughness. At midnight on the 12th of April, the fourth and fifth destroyer flotillas and the fourteenth torpedo flotilla reached Port Arthur roadstead, having with them under escort the mining ship, the _Koryo Maru_. The _Koryo Maru_ was a new vessel of 2,700 tons burden, specially constructed for torpedo and mining work. Captain Oda, the officer in command, was one of the ablest experts in this branch of warfare in the Japanese navy, and he had only recently been decorated for his distinguished services. He had invented a new type of mine of a particularly deadly description, and it was now to be tried for the first time in actual warlike operations. The work of laying the mines was entered upon without delay, and with all the customary daring and resource exhibited by the Mikado's sailors in this dangerous class of service. Notwithstanding the relentless glare of the searchlights, which threw the vessel into strong relief and made her the target for two hundred guns, Captain Oda and his men calmly went about their work unheeding. The torpedo-boats and destroyers in the meantime took up a position on the flanks of the _Koryo_ and endeavored to attract the fire of the fortress to themselves, while their escort was doing her deadly work unsuspected. The enterprise was aided by a renewal of the extraordinary feebleness and lack of skill which had so often been characteristic of the Russian defense in the past. Not only were the garrison gunners unable to hit the mark so plainly presented to them, but the torpedo flotilla, which, despite its recent losses, still constituted a formidable force, did nothing to interfere with operations which threatened so vitally the safety of the fleet. Even Admiral Makaroff seems to have been at fault on this occasion. It is almost inconceivable that the true nature of the _Koryo's_ proceedings was not guessed by him, and that the most active measures were not taken to put a stop to them. Whatever may have been the reason, however, nothing effective was done, and Captain Oda was able to complete his work unharmed in spite of the shells which were churning up the water all round him. It must be remembered, nevertheless, that the immunity which the _Koryo_ actually enjoyed is no measure of the risk that she ran. No more heroic and devoted act illumines the long history of naval warfare than the laying of these mines close to the harbor, and under the full fire of the enemy's guns, any one of whose missiles, by exploding the dangerous cargo, might have sent the ship to destruction in a moment. But, as it turned out, the _Koryo_ was saved by the bad gunnery of the Russians, and having performed his duty well