
During the early months of WW2, the Army Air Force had need of an "off the shelve" aircraft to press into service as a utility aircraft and coast line patrol aircraft. All the Lockheed model 18's which were in airline service at the time were "conscripted" into the military. This aircraft would lead to other designs by Lockheed, such as the Navy PV-1, B-34 and B-37, depending on which engine was installed, which was altogether a different aircraft than the model 18 and would see service though out the balance of the war. The PV-1 would go on to replace the Hudson bomber for the RAF, as a patrol aircraft because of faster speed and could carry more bombs for anti-submarine patrol duty.
As production lines were tooled up and started, the model 18 was modified for military use and started as the C-60 for the Army and R5-0 for the Navy. During the early months of 1942, the primary responsibility for anti-submarine warfare in the United States was shouldered by the Army Air Force. This irked the Navy, as it considered this region of battle its burden. To carry out such a task, the Navy was pursuing a long-range, land-based patrol and reconnaissance aircraft with a substantial bombload. This goal was always resisted by the Army Air Force, which carefully protected its monopoly on land-based bombing. This forced the navy to use long-range floatplanes for these roles. The Navy was unable to upgrade to more capable aircraft until the Army Air Force needed the Navy plant in Renton, Washington to manufacture its Boeing B-29 Superfortress. In exchange for use of the Renton plant, the Army Air Force would discontinue its objections to Naval land-based bombers, and provide aircraft to the Navy. One of the clauses of this agreement stated that production of the B-34 and B-37 by Lockheed would cease, and instead these resources would be directed at building a navalized version, the PV-1 Ventura.

The PV-1 Ventura, built by the Vega Aircraft Company division of Lockheed (hence the "V" Navy manufacturer's letter that later replaced the "O" for Lockheed), was a version of the Ventura built for the U.S. Navy (see Venturas in U.S. Navy service below). The main differences between the PV-1 and the B-34 were the inclusion of special equipment in the PV-1, adapting it to its patrol bombing role. The maximum fuel capacity of the PV-1 was increased from 1,345 gal (5,081 l) to 1,607 gal (6,082 l), to increase its range; the forward defensive armament was also reduced for this reason. The most important addition was of an ASD-1 search radar.
Early production PV-1s still carried a bombardier's station behind the nose radome, with four side windows and a flat bomb-aiming panel underneath the nose. Late production PV-1s dispensed with this bombardier position and replaced it with a pack with three 0.50 in (12.7 mm) machine guns underneath the nose. These aircraft could also carry eight 5 in (127 mm) HVAR rockets on launchers underneath the wings.
The PV-1 began to be delivered in December 1942, and entered service in February 1943. The first squadron in combat was VP-135, deployed in the Aleutian Islands in April 1943. They were operated by three other squadrons in this theatre. From the Aleutians, they flew strikes against bases in Paramushiro and Shimushu, Japanese islands in the Kurile chain. Often, PV-1s would lead B-24 bomber formations, since they were equipped with radar. In late 1943, some PV-1s were deployed to the Solomon Islands as night fighters with VMF(N)-531, a Marine Corps fighter squadron.
The last of these great Lockheed aircraft was the "Harpoon" or PV-2. e PV-2 Harpoon was a major redesign of the Ventura with the wing area increased from 551 ft² (51.2 m²) to 686 ft² (63.7 m²) giving an increased load-carrying capability, and which first flew on 3 December 1943. The motivation for redesign was weaknesses in the PV-1, since it had shown to have poor-quality takeoffs when carrying a full load of fuel. On the PV-2, the armament became standardized at five forward-firing machine guns. Many early PV-1s had a bombardier's position, which was deleted in the PV-2. Some other significant developments included the increase of the bombload by 30% to 4,000 lb (1,800 kg), and the ability to carry eight 5-inch (127 mm) HVAR rockets under the wings.
While the PV-2 was expected to have increased range and better takeoff, the anticipated speed statistics were projected lower than those of the PV-1, due to the use of the same engines but an increase in weight. The Navy ordered 500 examples, designating them with the popular name Harpoon.
Early tests indicated a tendency for the wings to wrinkle dangerously. As this problem could not be solved by a 6 ft (1.8 m) reduction in wingspan (making the wing uniformly flexible), a complete redesign of the wing was necessitated. This hurdle delayed entry of the PV-2 into service. The PV-2s already delivered were used for training purposes under the designation PV-2C. By the end of 1944, only 69 PV-2s had been delivered. They finally resumed when the redesign was complete. The first aircraft shipped were the PV-2D, which had eight forward-firing machine guns and was used in ground attacks. When World War II ended, all of the order was cancelled.
With the wing problems fixed, the PV-2 proved reliable, and eventually popular. It was first used in the Aleutians by VP-139, one of the squadrons that originally used the PV-1. It was used by a number of countries after the war’s end, but the United States ceased ordering new PV-2s, and they were all soon retired from service
The PV-1 began to be delivered in December 1942, and entered service in February 1943. The first squadron in combat was VP-135, deployed in the Aleutian Islands in April 1943. They were operated by three other squadrons in this theatre. From the Aleutians, they flew strikes against Paramushiro, a Japanese island. Often, PV-1s would lead B-24 bomber formations, since they were equipped with radar. In late 1943, PV-1s were deployed to the Solomon Islands and to the newly captured field at Tarawa in the Gilbert Islands.

This a pic of the Navy R50-6, same as Army C-60.
This aircraft was also used by President Getulio Vargas of Brazil as personal transport, and after the war, many of these aircraft were converted into "executive" transports by serveral companies such as Dalls Aero, Bill Lear's Learstar, (Lear would go on later to design and develop the "Learjet" executive jet aircraft and Howard Aero's, Howard 250, a very popluar converson of this aircraft.
