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The Martin B-12 was a
production version of the B-10 that was powered by
the Pratt & Whitney Hornet radial instead of the
Wright Cyclone. It was common in those days to
assign different USAAC model numbers to aircraft of
a given type which differed from each other only in
the type of engines which powered them.
On January 17, 1933,
the Army had ordered 48 production examples of the
Martin Model 139 monoplane bomber design. 32 of the
aircraft on this original order were ordered as
YB-12s and B-12As. They differed from the YB-10
primarily in being powered by Pratt and Whitney
R-1690-11 Hornet radials in place of the Wright
Cyclones of the B-10 series.
The first YB-12
appeared in February of 1934. Despite their new
model number, they were otherwise quite similar to
the YB-10. They could be externally distinguished
from the B-10 version by the presence of oil cooler
intakes on the port side of the engine nacelles.
Internally, the B-12A had provision for an extra
fuel tank in the bomb bay. This tank had a capacity
of 265 US gallons, supplementing the 226 US gallons
normal fuel capacity on long flights.
In January of 1931,
the US Army was assigned the responsibility for
coastal defense around the United States mainland.
As part of this mission, several Army B-12As were
fitted with large floats for water-based operations.
A B-12A fitted with twin floats set a seaplane speed
record on August 24, 1935.
The B-12s remained in
service with Army bombardment squadrons until the
advent of the B-17 and B-18 in the late 1930s. The
advances in bomber technology suddenly became so
rapid that the B-10/B-12 series of bombers,
revolutionary as they were at the time of their
appearance, swiftly became obsolete as the 1930s
progressed. By 1940, the B-10s and B-12s were
thoroughly out of date and had been largely
relegated to secondary roles such as target towing.
No US Army B-10Bs or B-12s participated in any
combat during World War 2.
Serials of B-12:
33-155/161 Martin YB-12
33-163/177 Martin B-12A
33-258/267 Martin B-12A
Specification of
Martin YB-12:
Two Pratt & Whitney
R-1690-11 Hornet air-cooled radial engines, rated at
700 hp at 6500 feet. Maximum speed 212 mph at 6500
feet, 190 mph at sea level. Initial climb rate 1740
feet per minute. An altitude of 10,000 feet could be
attained in 10.1 minutes. Cruising speed 170 mph.
Landing speed 71 mph. Service ceiling 24,600 feet.
Absolute ceiling 26,600 feet. Normal range 524
miles, maximum range 1360 miles, Weights: 7728
pounds empty, 12,824 pounds gross Dimensions:
wingspan 70 feet 6 inches, length 44 feet 9 inches,
height 15 feet 5 inches, wing area 678 square feet.
One 0.30-inch Browning machine gun in nose turret,
one 0.30-inch Browning machine gun in flexible mount
in dorsal gunner position, and one 0.30-inch
Browning machine gun in ventral tunnel. 2260 pounds
of bombs could be carried.
Sources:
- United States
Military Aircraft Since 1909, Gordon Swanborough
and Peter M. Bowers, Smithsonian, 1989.
- American
Combat Planes, Ray Wagner, Third Edition,
Doubleday, 1982.
- U.S. Army
Aircraft, 1908-1946, James C. Fahey
- Joe Baugher
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