[11] Following the outbreak of the First World War three years later, Aitken, as a temporary major-general, led the first notable incursion into German East Africa at the head of Indian Expeditionary Force B,[6] and was defeated at the Battle of Tanga in early November 1914.

[14] The German defence forces were led by Paul von Lettow-Vorbeck,[12] who held out until the end of the war.

In November 1921 the Secretary of State for India said in the House of Commons that Colonel Aitken had been retired on full pension with the rank of honorary brigadier-general, backdated to May 1918.

Because of poor health he spent his final months in Italy and died there suddenly of a heart attack.

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