Subject: Bomber series--Martin B-12

From: [email-masked]
Date: 5 Jul 94 16:25:42 GMT

>From [email-masked]

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 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.  
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.  

The first YB-12 appeared in February of 1934.  

A B-12A was fitted with twin floats and set a seaplane speed record on 
August 24, 1935.  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.  

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the B-10s and B-12s were thoroughly out of date and had been largely 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.  

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				AT&T Bell Laboratories
1000 E. Warrenville Road		Naperville, Illinois 60566-7013