Mackintosh's first Antarctic experience was as second officer on Shackleton's
Expedition "Nimrod", 1907<unk>1909. ️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️ 1909 he returned to participate in the later stages of the expedition; his will and determination in adversity impressed Shackleton, and led to his Ross Sea party appointment in 1914.