Aeneas Lionel Acton Mackintosh (1 July 1879 – 8 May 1916) was a British Merchant Navy officer and Antarctic explorer who commanded the Ross Sea party as part of Sir Ernest Shackleton's Imperial Trans-Antarctic Expedition, 1914–1917.

He returned in 1909 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.

His problems were compounded when the party's ship, SY Aurora, was swept from its winter moorings during a gale and was unable to return, causing the loss of vital equipment and supplies.

In carrying out the party's depot-laying task, one man died; Mackintosh barely survived, owing his life to the actions of his comrades who brought him to safety.

Restored to health, he and a companion disappeared while attempting to return to the expedition's base camp by crossing the unstable sea ice.

Shackleton commended the work of the party, and equated the sacrifice of their lives to those given in the trenches of the First World War, but was critical of Mackintosh's organising skills.

After serving a tough Merchant Officer's apprenticeship, he joined the P and O Line, and remained with this company until he was recruited by Shackleton's Nimrod expedition, which sailed for Antarctica in 1907.

[7] On 31 January 1908, not long after Nimrod's arrival at McMurdo Sound in the Antarctic, Mackintosh was assisting in the transfer of sledging gear aboard ship when a hook swung across the deck and struck his right eye, virtually destroying it.

He was immediately taken to the captain's cabin where, later that day, expedition doctor Eric Marshall operated to remove the eye, using partly improvised surgical equipment.

Shackleton, who had earlier fallen out with the ship's master, Rupert England, had wanted Mackintosh to captain Nimrod on this voyage, but the eye injury had not healed sufficiently to make this appointment possible.

[9] On 1 January 1909, on its return to Antarctica, Nimrod was stopped by the ice, still 25 miles (40 km) from the expedition's shore base at Cape Royds.

[14] Eventually, after stumbling around in the fog for hours, they fortunately encountered Bernard Day, a member of the shore party, a short distance from the hut.

John King Davis, then serving as Nimrod's chief officer, remarked that "Mackintosh was always the man to take the hundredth chance.

"[15] Mackintosh later joined Ernest Joyce and others on a journey across the Great Ice Barrier to Minna Bluff, to lay a depot for Shackleton's polar party, whose return from their southern march was awaited.

[10] On 3 March, while keeping watch on the deck of Nimrod, Mackintosh observed a flare, which signalled the safe return of Shackleton and his party.

[1] In February 1912, Mackintosh married Gladys Campbell, and settled into an office job as assistant secretary to the Imperial Merchant Service Guild in Liverpool.

"[1] He was therefore delighted, early in 1914, to receive an invitation from Shackleton to join the latter's Imperial Trans-Antarctic Expedition, which was to attempt the first transcontinental crossing of Antarctica.

The main party would establish a base in the Weddell Sea, from which a group of six led by Shackleton was to march across the continent, via the South Pole.

Eric Marshall, the surgeon from the Nimrod expedition, turned the assignment down, as did John King Davis;[20][21] Shackleton's efforts to obtain from the Admiralty a naval crew for this part of the enterprise were rejected.

[24] The task of dealing with these difficulties within a very restricted timescale caused Mackintosh great anxiety, and the various muddles created a negative image of the expedition in the eyes of the Australian public.

[30] On 16 January 1915, the shore party landed at McMurdo Sound, where Mackintosh established a base camp at Captain Robert Falcon Scott's old headquarters at Cape Evans.

[32] Joyce was shocked by the rebuff; he had expected that Mackintosh would defer to him on sledging matters: "If I had Shacks here I would make him see my way of arguing", he wrote in his diary.

A blizzard delayed their start,[34] a motor sledge broke down after a few miles,[35] and Mackintosh and his group lost their way on the sea ice between Cape Evans and Hut Point.

"[44] However, ice conditions in McMurdo Sound made it impossible for the ship to return; the shore party of ten was effectively marooned, with drastically depleted resources.

The party would seek to make up its lack of supplies and equipment by salvaging the stores left by earlier expeditions, particularly from Captain Scott's recent sojourn at Cape Evans.

This operation was the first stage in the process of laying down depots at intervals of one-degree latitude 60 nautical miles (110 km; 69 mi), down to Mount Hope at the foot of the Beardmore Glacier.

By 18 March, all five survivors were recuperating at Hut Point, having completed what Shackleton's biographers Marjory and James Fisher describe as "one of the most remarkable, and apparently impossible, feats of endurance in the history of polar travel.

[59] On 8 May 1916, after carrying out reconnaissance on the state of the sea ice, Mackintosh announced that he and Hayward were prepared to risk the walk to Cape Evans.

[62] Mackintosh is commemorated by a memorial on his mother Annie's grave in the churchyard of St John the Evangelist's Church in Burgess Hill, West Sussex.

[75] His son, Lord Shackleton, in a much later assessment of the expedition, wrote: "Three men in particular emerge as heroes: Captain Aeneas Mackintosh, ... Dick Richards, and Ernest Joyce.