modified, as well. Every Lightning from the P-38G onward was capable of being fitted with drop tanks straight off the assembly line. In March 1942, General Arnold made an off-hand comment that the US could avoid the German U-boat menace by flying fighters to the UK (rather than packing them onto ships). President Roosevelt pressed the point, emphasizing his interest in the solution. Arnold was likely aware of the flying radius extension work being done on the P-38, which by this time had seen success with small drop tanks in the range of , the difference in capacity being the result of subcontractor production variation. Arnold ordered further tests with larger drop tanks in the range of ; the results were reported by Kelsey as providing the P-38 with a ferrying range. Because of available supply, the smaller drop tanks were used to fly Lightnings to the UK, the plan called Operation Bolero. Led by two Boeing B-17 Flying Fortresses, the first seven P-38s, each carrying two small drop tanks, left Presque Isle Army Air Field in Maine on 23 June 1942 for RAF Heathfield in Scotland. Their first refueling stop was made in far northeast Canada at Goose Bay. The second stop was a rough airstrip in Greenland called Bluie West One, and the third refueling stop was in Iceland at Keflavik. Other P-38s followed this route with some lost in mishaps, usually due to poor weather, low visibility, radio difficulties, and navigational errors. Nearly 200 of the P-38Fs (and a few modified Es) were successfully flown across the Atlantic in July–August 1942, making the P-38 the first USAAF fighter to reach Britain and the first fighter ever to be delivered across the Atlantic under its own power. Kelsey himself piloted one of the Lightnings, landing in Scotland on 25 July. Operational history The first unit to receive P-38s was the 1st Fighter Group. After the attack on Pearl Harbor, the unit joined the 14th Pursuit Group in San Diego to provide West Coast defense. Entry to the war The first Lightning to see active service was the F-4 version, a P-38E in which the guns were replaced by four K17 cameras. They joined the 8th Photographic Squadron in Australia on 4 April 1942. Three F-4s were operated by the Royal Australian Air Force in this theater for a short period beginning in September 1942. On 29 May 1942,