 Apo Hondo yeSpain neAmerica yakatanga muna May 1898, Sumner akagadzwa kuva brigadier general wevazvipiri ndokuiswa mukutonga kwe1st Brigade, Cavalry Division, V Corps. Akatumirwa kuCuba pamwe chete neboka racho uye akatungamirira boka rake kuti rishande muHondo yeLas Guasimas. Apo Joseph Wheeler akarwara, Sumner akatora kwenguva pfupi kutungamira kweCavalry Division. Akanga achiri mutungamiriri weboka apo kurwisana paHondo yeSan Juan Hill kwakatanga. Zvisinei, kunotaurwa kuti apo Wheeler akanzwa ruzha rwehondo akasimuka pamubhedha wake wokurwara ndokumhanyira kutora kutonga kwechikamu. Sumner akadzoka kuzotungamira brigade rake kwehondo yose uye muKukombwa kweSantiago. Muna September, akagadzwa kuva mukuru mukuru wevazvipiri. Akadzingwa muzvipiri ndokudzokera kuchinzvimbo chake cheRegular Army checolonel musi waApril 15, 1899. 