Halswelle, by then a captain, was killed by a sniper at the Battle of Neuve Chapelle in France, during World War I, on 31 March 1915 aged 32 while attempting to rescue an injured fellow officer. Earlier in the same battle (12 March) he was hit by shrapnel or shell fragments while leading his men across an area known as Layes Brook but despite his wounds he refused to be evacuated and continued at the front, although heavily bandaged.