Whakaotihia te rerenga e whai ake nei: I te tau 1898, ka kitea e Rynning kua tīmata te pakanga ki Paniora, ā, kei te whakaarahia e tana hoa tawhito, e Colonel Leonard Wood, tētahi rārangi kaieke hoiho tūao, i muri mai ka mōhiotia ko Theodore Roosevelt's Rough Riders. I whakauruhia ia hei tangata takitahi ka hoki mai i te pakanga hei tuarua tuarua i roto i te Troop B, 1st United States Volunteer Cavalry Regiment. I roto i te
I te Pakanga o San Juan Heights, i riro i a Rynning te mana o te raina Amerika whai muri i te matenga o Kapene Buckey O'Neill. I etahi meneti i muri mai ka arahi ia i nga Rough Riders ki runga ki Kettle Hill a ko ia te Amerikana tuatahi i eke ki te tihi. I raro i te pupuhi kaha mai i te pukepuke San Huan tata, i whakahau a Rynning i ana tangata ki te whakaoho i te haki o te rerenga ki te whakakotahi i etahi atu, a i tenei wa ka kino te haki. Kei te tiakina te haki e te Tari o te Whare Pukapuka me nga Pūranga i te whare rangatira o te kawanatanga i Phoenix, Arizona. Whai muri i tera, ka uru atu a Rynning ki a Theodore Roosevelt ki te whakapae i San Juan Hill, i mutu ai te pakanga me te wikitoria a Amerika.