In August of 1941, large orders for Lockheed Venturas were placed with Lend-Lease funds. These planes would be owned by the US Government but would be "leased" or "lent" to Britain and its allies in support of their war effort against Germany. Among the orders that had been placed at that time was a contract for 550 armed reconnaissance versions of the Ventura to be built in Lockheed's B-1 plant under the designation O-56-LO (company designation Model 137-96-03). Serial numbers were 41-37470/38019.
The O-56 differed from the B-34 primarily in being powered by a pair of 1700 hp Wright R-2600-13 air-cooled radials instead of 2000 hp Pratt & Whitney R-2800 radials. However, before the first O-56 could be completed, the USAAF had dropped the O-for-observation designation category, and the O-56 had been redesignated RB-34B-LO. Before the first RB-34B-LO could fly, the USAAF had redesignated the plane once again, this time to B-37-LO. The fact that different engines were being used was thought to justify a new bomber series number.
Aside from the engines, the B-37 was almost identical to the B-34. However, the B-37 could be externally distinguished from the B-34 by the presence of two oval waist gun ports on either side of the rear fuselage for a single 0.30-inch flexible machine gun.
During the early months of 1942, the USAAF had assumed the primary responsibility for flying antisubmarine patrols over the Atlantic Ocean in support of the battle against German U-boats. This was a thorn in the side of the US Navy, since that service had always felt that antisubmarine warfare was its responsibility. In order to carry out this mission, the Navy was anxious to acquire a long-range, land-based heavy maritime reconnaissance and patrol aircraft capable of carrying a substantial bombload. However, the USAAF had always resisted what it perceived as an encroachment by the Navy into its jealously-guarded land-based bomber program, and forced the Navy to rely on long-range floatplanes such as the PBY Catalina, the PBM Mariner, and PB4Y Coronado to fulfill the long-range maritime reconnaissance role. However, the USAAF needed an aircraft plant to manufacture its next generation of heavy bombers, the B-29 Superfortress. It just so happened that the Navy owned a plant at Renton, Washington, which was at that time being operated by Boeing for the manufacture of the PBB-1 Sea Ranger twin-engined patrol flying boat. The Army proposed that the Navy cancel the Sea Ranger program and turn over the Renton factory to them for B-29 production. In exchange, the USAAF would agree to get out of the antisubmarine warfare business and would drop its objections to the Navy's operation of land-based bombers. In support of the Navy's new land-based antisubmarine patrol mission, it was proposed that the Navy be permitted acquire navalized versions of the B-24 Liberator and the B-25 Mitchell. In addition, it was proposed that Lockheed cease all production of B-34/37 Venturas for the USAAF and start building a navalized version of the Ventura for the Navy under the designation PV-1 for use in maritime reconnaissance and antisubmarine warfare. The Navy readily agreed to this arrangement.
On July 7, 1942, the USAAF agreed to discontinue procurement of B-34/B-37s so that Lockheed Vega could concentrate on the production the PV-1. Manufacture of the B-37-LO ceased after the completion of only 18 examples (41-37470/37487). The Ventura III designation had been reserved for the RAF delivery of the O-56-LO, but since the O-56 never materialized, this designation was never used.
41-37470/38019 Lockheed B-37-LO Only 37470/37487 built (c/n 437-6476/6493).
Engines: Two 1700 hp Wright R-2600-13 air-cooled radials. Maximum speed 298 mph at 13,500 feet. Cruising speed 198 mph. An altitude of 10,000 feet and could be attained in 5.5 minutes. Service ceiling 22,400 feet. Normal range 1300 miles. Maximum range 2700 miles. Dimensions: Wingspan 65 feet 6 inches, length 51 feet 5 inches, height 11 feet 11 inches, wing area 551 square feet. Weights: 18,615 pounds empty, 27,000 pounds loaded, 29,500 pounds maximum. Armament: Two 0.50-inch machine guns installed in dorsal turret. A pair of flexible 0.30-inch machine guns were mounted in a ventral position behind the wing trailing edge. Two fixed forward-firing 0.50-inch machine guns were installed in the upper decking of the nose. One 0.30-inch machine gun in a lower waist position on each side of the rear fuselage. A bomb load of 3000 pounds could be carried in an internal bomb bay.