By a royal warrant of 13 May 1690, Romer was appointed engineer in Ireland at 20 shillings a day, to commence from 1 March 1689. He took part in the campaigns of 1690 and 1691, and was employed on the fortifications of Cork, Longford, and Thurles. He remained in Ireland until 1692, when he was appointed by royal warrant of 7 July, chief engineer of the artillery train fitted out at St. Helen's for the expedition against the coast of France. On 26 July he embarked with fourteen thousand troops in transports, and joined the fleet at Portland, when the expedition was abandoned. In 1693, he was chief engineer of the ordnance train of the expedition to the Mediterranean; he served under Richard Coote, 1st Earl of Bellomont, and embarked in the fleet under Delaval, Killigrew, and Rooke, to convoy the so-called Smyrna fleet. On 8 May 1694, he was directed by royal warrant to report on the defences of Guernsey, and to lay out any additional works which were urgent. A plan of Castle Cornet, drawn by Romer when on this duty, is in the British Museum.