On the outbreak of the First World War he served on the Western Front before joining Major-General Beauvoir De Lisle’s 1st Cavalry Division staff. He followed De Lisle to Gallipoli when the latter took command of the 29th Division. Hardress Lloyd was appointed second in command of the 1st Battalion Royal Inniskilling Fusiliers in May 1916, becoming its commanding officer a month later. Whilst commanding this battalion he was awarded the DSO in January 1917. In February 1917 he was appointed commander of D Battalion, one of the founding units of the Heavy Branch Machine Gun Corps.