We describe the case of a 23-year-old serviceman on overseas deployment who presented with a painful, swollen arm. Investigations showed an upper extremity deep vein thrombosis (UEDVT) of the right arm with an associated asymptomatic pulmonary embolism, which was treated with warfarin anticoagulation. Further investigation identified positional obstruction at the thoracic outlet, and the patient was diagnosed with Paget–Schroetter syndrome. He underwent elective resection of the first rib, and has now returned to normal duties. After review of the literature on UEDVT, it is suggested that in this military patient, the occurrence of an anatomical variant put him at risk of upper limb venous thrombosis, which was probably potentiated by the occupational factor of carrying a rifle. The external compression of the subclavian vein from the rifle butt and hypertrophied muscles, in addition to the anatomical variation, caused repetitive microtrauma of the vessel intima, which precipitated venous thrombosis.