"Winston Churchill watching a Short Stirling bomber of No. 7 Squadron taking off, 6 June 1941." Prime Minister Winston Churchill watches a Short Stirling heavy bomber of No 7 Squadron, Royal Air Force. The four-engined Short Stirling first saw service in August 1940 but its relatively low operational ceiling of 17,000 feet made it more vulnerable to enemy defences than the Halifaxes and Lancasters.