Captain Jack (Updated: 8/31/2016):
The Lancaster design was given an increased high-aspect ratio wingspan along with an elongated fuselage assembly and a new nose to produce the Lancaster B.Mk IV. The nose accommodated a Boulton Paul powered turret fitting 2 x .50 caliber Browning heavy machine guns. Initial models were fitted with 4 x two-stage Rolls-Royce Merlin 85 series inline engines of 1,750 horsepower each housed in underslung nacelles, two engines to a wing. The B.Mk IV then became the start of the new Lincoln series of heavy bombers as the Lincoln B.Mk I. Following another increase in wingspan and a further lengthening of the fuselage, the Lincoln B.Mk II model was born and these were powered by 4 x Rolls-Royce Merlin 66, 68A or 300 inline engines throughout their service lives.
First flight of a Lincoln prototype occurred on June 9th, 1944, now designed to Air Ministry Specification 14/43. Three prototypes would eventually be built under the company designation of Type 694. The aircraft showcased an increased operational range as well as an improved operational service ceiling which allowed it to operate further from friendly bases and farther from enemy ground attack installations. The Lincoln was quickly adopted by the RAF and production lines set up at three Avro facilities in Chadderton, Cheshire and Woodford. To help with wartime demand for such aircraft, Armstrong Whitworth and Vickers Metropolitan both were eventually awarded with additional manufacture of the Avro product. The Royal Australian Air Force (RAAF) was eventually granted local license production of the Lincoln I to which it knew as the Lincoln B.Mk 30 and modified with Rolls-Royce Merlin 85 engines. However, these did not appear until after the war.
Outwardly, the Lincoln looked very much as an enlarged Lancaster. The design centered along the boxy squared-off tapered fuselage form to which high-mounted wings and a split-vertical tail fin was added. Each wing managed a pair of engines in streamlined nacelles and within easy view of the crew. The cockpit consisted of a heavily glazed covering with the crew set slightly aft of the nose. The nose was also windowed and sported the typical Avro bulb-like shape. The undercarriage was made up of two main landing gear legs, each mounting a large donut-style wheel, while the tail was supported by a single-wheeled leg. This gave the Lincoln a pronounced "nose-up" appearance when at rest. The internal bomb bay took over a large internal portion of the fuselage, the doors running from under the flightdeck to amidships. The standard operating crew involved seven personnel made up of two pilots, the navigator, radio operator, bombardier/nose gunner, a dorsal gunner and a tail gunner.
The Lincoln was defensed through a network of machine gun fittings. This included a nose turret with 2 x 0.50 caliber machine guns, a tail turret with 2 x 0.50 caliber machine guns and a dorsal turret with either 2 x 0.50 caliber machine guns or 2 x 20mm Hispano cannons. The internal bomb load capacity of the original B.Mk I was approximately 14,000lbs under general conditions.