"The Polish Air Force in Britain, 1940-1947" Instructor of No. 18 Operational Training Unit lectures Polish airmen on the .303 Vickers K-type gas-operated machine gun during a detachment to No. 9 Bombing and Gunnery School at Penrhos, Caernarvonshire. 18 OTU was formed from the Polish Training Unit in No. 6 Group, Bomber Command, in June 1940, to train light bomber crews for Polish operational squadrons.