An improved version of the Martin MB-1, the MB-2, was ordered by the USAAS in June of 1920. This model had new and larger wings that were intended to make it possible to carry a heavier bomb load. In the MB-1, the Liberty engines were suspended between the wings by a system of struts, but on the MB-2, the twin Liberty engines were lowered to sit inside nacelles attached to the lower wing. As compared to the MB-1, the landing gear was simplified to only two wheels. The non-staggered wings were hinged at the rear spars just outboard of the engines, and could be folded aft for storage. The armament consisted of five Lewis 0.50-in machine guns, two in the front cockpit, two in the rear, and one aimed downwards and to the rear. A crew of four could be carried.
The first flight of the MB-2 (serial number AS 64195) took place on September 3, 1920. The MB-2 was designed specifically as a night bomber, and sacrificed the high speed and maneuverability of the MB-1 for a greater bombload. Ten MB-2s were built by the Glenn L. Martin company in Cleveland, and were redesignated NBS-1 when the new Army designation scheme was introduced. Their serials were 64195/64214. These planes are best remembered today as being the aircraft which participated in the famous Billy Mitchell demonstration of July 21, 1921 in which the ex-German battle cruiser *Ostfreisland* was sunk by aerial bombardment. Special 2000-pound bombs had to be designed for the test.
Martin proposed to the Army that 50 more NBS-1 bombers be built. However, under the prevailing policy of the time, the rights to the NBS-1 design were owned by the Army rather than by Martin. Consequently, the Army had the right to ask for competitive bids on the project from other manufacturers. In 1921, Curtiss underbid the Glenn L. Martin Co. for the production of 50 examples of the NBS-1. In order to spread scarce military procurements among as many manufacturers as possible, contracts for 35 other NBS-1s were granted to the L.W.F. (Lowe, Willard, and Fowler) Engineering Company of College Point, New York and a contract for 25 more was granted to the Aeromarine Plane and Motor Co. of Keyport, New Jersey.
The last 20 Curtiss-built NBS-1 bombers were equipped with General Electric turbosuperchargers. These were the first airplanes to use turbosuperchargers in production quantities. With these turbosuperchargers, the NBS-1 could reach a service ceiling of 25,341 feet. However, the use of turbosuperchargers in bombers proved to be premature, the early superchargers being notoriously unreliable. Practical application of turbosuperchargers to bombers did not take place until the B-17B of 1939.
Eight Army bombing squadrons used the NBS-1--the 11th, 20th, 49th and 96th Squadrons with the 2nd Bomb Group based at Langley Field in Virginia, the 23rd and 72nd Squadrons with the 5th Composite Group in Hawaii, and the 28th Squadron with the 4th Composite Group in the Philippines. They remained in service until replaced by Keystone bombers in 1928-29.
Serials of NB-2/NBS-1:
Martin MB-2 64195/64214 L.W.F. NBS-1 68437/68471 Curtiss NBS-1 68478/68527 Aeromarine NBS-1 22-201/225
Specification of Martin NBS-1:
Two 420hp Liberty 12 liquid-cooled Vee engines. Maximum speed 99 mph at sea level. Cruising speed 92 mph. Landing speed 59 mph. Initial climb rate 391 feet per minute. Service ceiling 8500 feet. Maximum ceiling 9900 feet. Range 400 miles with 2000 pounds of bombs. Maximum range 558 miles. Wingspan 74 feet 2 inches, length 42 feet 8 inches, height 14 feet 8 inches, wing area 1121 square feet Armament consisted of five 0.30-inch machine guns. An internal bombload of up to 1800 pounds could be carried. Instead of the internal bombload, an external bombload of up to 2000 pounds could be carried.