On the outbreak of World War 1 the Nyasaland Administration Gunboat was ordered to "sink, burn or destroy" the German gunboat which presented a threat to shipping on Lake Nyasa.. Finding her hauled out at the German port of Sphinxhaven on the 13th August 1914 the Guendolen rendered her inoperable in the first maritime engagement of World War 1.

Commander Rhoades received his orders from the Governor Sir George ‘Utility’ Smith from Zomba and prepared to sail, on 8th August 1914, from the shipyard north of Fort Johnston (today Mangoche). With Dr Sanderson the MO and 2 L/t (temporary) Beaumont, Nyasaland Volunteer Reserve, and a section of 1 KAR were embarked. They sailed for Nkata Bay some 350 miles north arriving there on the 11th to hear that the Wissmann had recently been at Sphinxhaven where she had been hauled out for some plates to be replaced. Hoping she might still be there they sailed for Sphinxhaven overnight on the 12th arriving at dawn the following day. Knowing that the Wissman had a 1lb cannon and not having any other information the Guendolen opened fire at 2,000 yards. Unfortunately much of her Victorian ammunition was faulty and only one in four rounds detonated they scored only one hit on the slip way. The Captain of the "Hermann Von Wissmann," an old drinking colleague of Rhoades, not having heard that war had been declared, had his engineer row him out to the Guendolen in a dinghy to find himself a Prisoner of War. The KAR detachment was landed together with the engineers of the Guendolen who removed essential elements of the Wissmann rendering her immobile. Returning overnight to Chintechea signal reporting the success of the expedition was sent to Zomba and a report appeared in the Times the following day headlined ‘Naval Victory on Lake Nyasa,’ the first maritime engagement of World War 1.

With the removal of the threat posed by the Von Wissmann the Nyasaland Administration were able to reinforce Karonga at the north end of Lake Nyasa with impunity, and thereby defeat the German invasion which took place the following month.