Subject: Bomber Series--Martin B-10

From: [email-masked]
Date: 27 Jun 94 16:13:36 GMT

>From [email-masked]

The Martin B-10 was the first all-metal monoplane bomber to enter full 
production for the US Army.  It was also the first bomber to have a 
performance that exceeded that of contemporary pursuit aircraft.  

The immediate ancestor of the B-10 was the Martin 123, which was 
designed and built as a private venture by the Glenn L. Martin 
Company of Baltimore, Maryland.  It was a midwing all-metal monoplane.  
The monocoque fuselage had corrugated top and bottom surfaces with a 
deep belly.  The deep belly carried doors for an internal bomb bay, so 
the bombs could be carried internally rather than on external racks as 
in the Boeing YB-9.  The main landing gear retracted backwards into 
the rear of the engine nacelles, but the lower half of the wheels 
remained exposed.  Four crew members were to be carried.  Three of the 
crew members were seated in separate open cockpits on the top of the 
fuselage.  The nose gunner/bombardier had a transparent aiming 
position in the lower nose, the pilot sat in an open cockpit abreast 
of the forward wing, and the rear gunner sat in an open position in 
the rear dorsal fuselage.  The fourth crew member occupied a position 
inside the fuselage.  

The Model 123 flew for the first time at Baltimore on February 16, 
1932.  It was powered by a pair of 600 hp Wright SR-1820-E Cyclone 
engines that were enclosed by NACA low-drag cowling rings.  The 
wingspan was 62 feet 2 inches.  The Model 123 was delivered to the 
Army on March 20, 1932 under a bailment contract.  Although still 
Martin property, the aircraft was assigned the designation XB-907 for 
its trials at Wright Field.  Trials began in July of 1932.  

During the trials at Wright Field, a maximum speed of 197 mph was 
recorded at an altitude of 6000 feet.  This was truly spectacular 
performance for 1932.  

The Model 123 was returned to the factory in Baltimore for 
modifications.  During the early autumn of 1932, the open-cockpit gun 
position in the nose of the Martin 123 was replaced by a front gun 
turret.  This was a transparent, manually-rotated affair, with a 
single 0.30-inch machine gun.  The pilot's cockpit and the dorsal 
gunner position remained open.  At the same time, more powerful 675 hp 
R-1820-19 Cyclone engines were installed.  These engines were also 
fitted with full cowlings that extended forward of the wings.  A new 
longer-span wing was fitted, increasing the wingspan to 70 feet 7 
inches.  The designation was changed to XB-907A when it was returned 
to Wright Field for more tests.  

Trials of the XB-907A took place at Wright field in October of 1932.  
Despite an increase of nearly 2000 pounds in the gross weight to 
12,230 pounds, the XB-907A had a maximum speed of 207 mph at 6000 
feet.  The XB-907A was faster than any US fighter then in service.  
The Model 123 was a truly revolutionary design, and every other bomber 
in the world (and just about every pursuit plane as well) was 
instantaneously made obsolete.  In 1932, Martin was awarded the 
Collier Trophy for its work.  

On January 17, 1933, the Army purchased the XB-907A under the 
designation XB-10.  The serial assigned was 33-139.  At the same time, 
the Army ordered 48 production examples of the Martin design.  These 
were designated Model 139 by the factory.  

The first 14 aircraft were designated YB-10 (33-140/153).  They were 
powered by 675 hp Wright R-1820-25 engines.  They differed from the 
prototype primarily in having transparent sliding canopies fitted over 
both the pilot's cockpit and the rear gunner's position, a concession 
to the 200 mph-plus speeds that could be attained.  The rear cockpit 
was modified to accommodate a radio operator in addition to the 
gunner.  Armament consisted of a 0.30-inch Browning machine gun in the 
nose turret, a 0.30-inch gun in a flexible position in the dorsal 
position, plus a 0.30-inch machine gun in a tunnel position in the 
fuselage floor behind the bomb bay to guard against attacks from 
below.  The internal bomb bay could carry two 1130-pound bombs or five 
300-pound bombs.  There were provisions for an external shackle under 
the right wing for a single 2000 pound bomb.  The YB-10 could be 
distinguished from its successors by the presence of an oil cooler 
scoop on top of the engine cowling.  

A single YB-10A (33-154) was included in the 48 aircraft of the 
original order.  It was delivered in June of 1934 with a pair of 
experimental turbosupercharged R-1820-21 Cyclones.  It achieved a 
maximum speed of 236 mph at 25,000 feet.  Despite the high performance 
that was achieved, the turbosuperchargers were not sufficiently 
reliable to be introduced into production models.  Consequently, there 
was no B-10A production model, the first production model of the B-10 
series being the B-10B.  

Another experimental version included in the original order was the 
XB-14 (33-162), which was similar to the YB-10 but was powered by a 
pair of 950hp Pratt & Whitney YR-1830-9 Twin Wasps.  It was common in 
those days to assign a separate model number to aircraft which 
differed from each other only in the type of engine which powered 
them.  

The remaining 32 aircraft on the original order were delivered as 
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.  Despite their new model number, they were otherwise quite 
similar to the YB-10.  They will be described more fully in a later 
post.  

The first YB-10 was delivered to Wright Field in November of 1933.  
Most of the YB-10s were based at March Field in California with the 
7th Bomb Group until December of 1934, when it reequipped with B-12s.  
The YB-10s then remained at March with the 19th Bomb Group.  In a 
demonstration of their reliability and efficiency, ten YB-10s 
undertook a survey flight to Alaska in July of 1934.  

Production of the Martin bomber was continued by FY 1934 and 1935 Army 
procurements for 103 examples of the B-10B, the primary service 
version.  The B-10B could be distinguished from the YB-10 by the 
presence of air intakes on top the nacelle as well as by the 
relocation of the exhaust pipes from the lower nacelle to outlets at 
the nacelle top immediately behind the air intakes.  It was otherwise 
quite similar to the service test YB-10.  

The first B-10B arrived at Wright Field in July of 1935.  Production 
deliveries to Langley Field began in December of 1935 and were 
completed by August of 1936.  The B-10B served with the 2nd Bomb Group 
at Langley and the 9th at Mitchel Field.  The B-10B served (along with 
YB-10s) with the 19th Bomb Group based at March Field in California.  
The B-10B also served with the 6th Bomb Group based in the Canal Zone, 
and was issued to the 28th Bomb Group based in the Philippines.  

Army records do show that two aircraft designated simply B-10 were 
ordered as part of the the original B-10B contract, with serials 
36-347/348 being assigned.  They may have been replacements for the 
two experimental models (YB-10A, XB-14), but it is uncertain if these 
were actually delivered and, even if they were, in what particular 
configuration.  

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 YB-10s were fitted with large floats for 
water-based operations.  

The B-10s 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, 
revolutionary though it was, swiftly became obsolete as the 1930s 
progressed.  By 1940, the B-10B was thoroughly out of date and had 
been largely relegated to secondary roles such as target towing.  No 
US Army B-10Bs participated in any combat during World War 2.  

With such an advanced performance, the Martin company fully expected 
that export orders for the B-10 would come flooding in.  However, 
since the Army owned the rights to the Model 139 design, it forbade 
any export overseas until its own orders had been filled.  However, 
following the completion of the last example for the Army in 1936, 
clearance was finally given for the export of the Martin bomber.  

The first export demonstrator, the Model 139W, was completed in August 
of 1936.  It was powered by a pair of 750 hp Wright R-1820-F53 
Cyclones.  The civilian registration number NR-15563 was applied.  It 
was sent to Argentina in September to compete against the German 
Junkers JU-86 and the Italian Savoia SM-79B for Argentine orders.  The 
Martin plane won the contract, and Argentina ordered 13 examples for 
the Navy and 26 for the Army.  

Other export orders soon followed.  The Martin 139WC was a version 
intended for China.  It was powered by a pair of 850 hp R-1820-G2 
Cyclones.  6 examples went to China in February of 1937.  They were 
used in combat when Japan invaded China in August of 1937.  These 
Martin 139WCs were the first American-designed bombers to see combat.  
However, the results were not all that good, since most were destroyed 
on the ground during Japanese air attacks.  

Six Martins were sold to Siam in April of 1937.  They were powered by 
R-1820-G3 Cyclones.  20 Model 139Ws were sold to Turkey in September 
of 1937, powered by R-1820-G2 engines 

A single Model 139WR (X16706) was sold to the Soviet Union for 
evaluation.  Its fate is unknown.  

Plans to sell Martin 139s to Republican Spain were blocked by the 
State Department.  Reports that the Martin bomber was being used in 
Spain on the Republican side were in error, being misidentifications 
of the Soviet Tupolev SB-2, which was basically similar in overall 
configuration.  

The largest customer for the export Martin bomber was the Dutch East 
Indies.  The first Dutch order was for 12 Model 139WH-1 bombers 
powered by 750 hp R-1820-F53 Cyclones.  They were delivered between 
September 1936 and February 1937.  26 Model 139WH-3s, powered by 840 
hp R-1820-G3s were delivered from November 1937 to March 1938.  The 
final export version was the Model 139WH-3 (or Model 166), powered by 
a pair of 900 hp Wright R-1820G-102 radials.  It had a long unbroken 
transparent canopy "greenhouse" that extended from the pilot's cockpit 
all the way to the rear gunner's position.  78 of these new bombers 
were delivered by May 5, 1939, when the last export Martin bomber 
rolled off the Baltimore production line.  

Between mid-1936 and 1939, a total of 189 export Model 139W and Model 
166 bombers had been manufactured.  

Six squadrons of Martin bombers were serving in the Dutch East Indies 
when the Japanese invaded.  Dutch crews flew these Martin bombers in a 
futile attempt to stem the Japanese advance into the Dutch East Indies 
during early 1942.  By this time, the Martin bomber was thoroughly 
obsolete, and its speed and armament were completely inadequate to 
protect against fast and heavily-armed Japanese Zero fighters.  Most 
were shot down in combat or were destroyed on the ground.  

A surviving export Model 139 fled from the Dutch East Indies to 
Australia on March 7, 1942.  It was taken on strength by the USAAF for 
use as an utility aircraft and assigned the serial number 42-68358.  
This was the only export Martin 139 to serve with the USAAF.  

An Argentine Martin Model 139 was returned to the USA in 1976.  It was 
refurbished as a standard USAAC B-10B and is now on display in the Air 
Force Museum at Wright-Patterson AFB in Ohio.  So far as I am aware, 
it is the only surviving Model 139 bomber.  

33-139 		Martin XB-10 
33-140/153 	Martin YB-10 
33-154 		Martin YB-10A 
33-155/161 	Martin YB-12 
33-162 		Martin XB-14 
33-163/177 	Martin B-12A 
33-258/267 	Martin B-12A 
34-028/115 	Martin B-10B 
35-232/246 	Martin B-10B 
36-347/348 	Martin B-10 (not certain that these were delivered) 
42-68358 	Martin B-10 (ex-Dutch Model 139 impressed by USAAF)

Specification of Martin B-10B: 

Two Wright R-1820-33 Cyclone air-cooled radial engines, rated at 775 
hp for takeoff and 750 hp at 5400 feet.  Maximum speed 213 mph at 
10,000 feet, 196 mph at sea level.  An altitude of 5000 feet could be 
attained in 3.4 minutes.  Cruising speed 193 mph.  Landing speed 65 
mph.  Service ceiling 14,200 feet.  Normal range 590 miles, maximum 
range 1240 miles, ferry range 1830 miles.  Weights: 9681 pounds empty, 
14,600 pounds gross, 16,400 pounds maximum.  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 a ventral 
tunnel position mounted in the floor of the fuselage behind the bomb 
bay.  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