[7] During the Second Boer War, Swannell served in the British Army in South Africa, rising to the rank of lieutenant.

Promoted to major on 1 January 1915, he was killed on 25 April 1915 while taking part in the Landing at Anzac Cove, during the first day of the Gallipoli Campaign.

[14] On his return to Britain, Swannell joined the British Army and served in South Africa during the Second Boer War,[15] where he was commissioned as a lieutenant in the 35th Battalion (Buckinghamshire) Imperial Yeomanry on 20 January 1902.

[16] He returned to the UK with his battalion on the SS Orotava in December 1902,[17] and retained the rank of honorary lieutenant when he resigned his commission on 3 February 1903.

[18] It was reported that during his time in South Africa, he was personally recommended on the field for a commission by General Lord Methuen.

A keen all-round sportsman he coached not only rugby but also hockey, was vice-president of the Sydney Swimming Club,[14] and training senior military cadets for surf life-saving examinations.

[22] His poor personal hygiene and overly violent playing style,[22] made him an unpopular character in the eyes of other players.

Swanell played in 17 matches of the tour including three of the four Tests against the Australian national team, missing only the opening defeat.

[3][25] Swannell scored in only one game on the tour, a try in a win over the New South Wales Waratahs on 29 July 1899.

The British Isles were victorious over the Australians, but lost the New Zealand match, this was the first international game that Swannell had been on the losing side.

[37] He was vocal in his support for maintaining the amateur nature of rugby,[38] but did not side with Bedell-Sivright in denying that a stipend had been paid during the 1904 tour.

[22][45] In the buildup to the assault on the hill known as Baby 700, Swannell and his men were pinned down under heavy enemy fire.