The naval actions of the war were therefore of the nature of outpost raids and skirmishes rather than of battles. The first that developed any serious fighting took place in the Bight of Heligoland on 28 August. Apparently with the design of inducing the Germans to come out, a flotilla of submarines under Commodore Keyes was sent close in to Heligoland, with some destroyers and two light cruisers, the Arethusa and Fearless, behind them, and more substantial vessels out of sight in the offing. Presently there appeared a German force of destroyers and two cruisers, the Ariadne and the Strassburg; they were driven off mainly by the gallant fighting of the Arethusa; but thinking there was no further support the Germans then sent out three heavier cruisers, the Mainz, the Koln, and apparently the Yorck. The Arethusa and Fearless held their own for two or three hours until Beatty's battle-cruisers, led by the Lion, came safely through the German mine-fields and submarines to their assistance. The Lion's 13.5-inch guns soon settled the issue: the Mainz and the Köln were sunk, while no British unit was lost, and the casualties were 32 killed and 52 wounded against 300 German prisoners and double that number of other casualties. The overwhelming effect of heavier gunfire had been clearly demonstrated, and it was further illustrated on 17 October by the destruction of four German destroyers off the Dutch coast by the light cruiser Undaunted accompanied by four British destroyers; but the next exhibition of naval gun-power was to be at our expense. Among the incidental advantages which the adhesion of Great Britain brought to the Entente was the intervention of Japan, which, apart from its alliance with us, had never forgiven Germany the part she took in depriving Japan of the fruits of her victory over China in 1894, and regarded as a standing offence the naval base which Germany had established at Tsingtau and the hold she had acquired on North Pacific islands. On 15 August Japan demanded within eight days the surrender of the lease of Tsingtau and the evacuation of Far Eastern waters by German warships. No answer was, of course, returned, but the German squadron under Von Spee wisely left Tsingtau in anticipation of its investment by the Japanese. It began on the 27th, and troops were landed on 2 September: on the 23rd a British contingent arrived from Wei-hai-wei to co-operate, and gradually the lines of investment and the heavy artillery were drawn closer. The final assault was fixed for 7 November, but the Germans forestalled it by surrender; there were 3000 prisoners out of an original garrison of 5000, and Germany's last overseas base, on which she had spent £20,000,000, passed into the enemy's hands. Australian troops had already occupied without serious opposition German New Guinea, the Bismarck archipelago, and the Gilbert and Caroline Islands, while Samoa surrendered to a New Zealand force, and the Marshall Islands to the Japanese.