Subject: Bomber Series--North American B-25 Mitchell (6 of 32)

From: [email-masked] (Joe Baugher)
Date: Tue, 10 Jan 1995 03:19:58 GMT

The B-25C was the first version of the Mitchell to be mass-produced.  
Following the completion of the initial B-25, B-25A, and B-25B 
contracts, a number of contracts were awarded to North American for 
1625 B-25Cs to be built at its Inglewood factory.  At the same time, 
an additional contract was issued for 2290 essentially identical 
B-25Ds, to be built at a new North American plant in Kansas City, 
Kansas.  

The first B-25C contract was approved on September 24, 1940 for 863 
aircraft under the company designation NA-82.  On June 24, 1941, the 
Netherlands government ordered an additional 162 aircraft under the 
designation NA-90 which were later built as the B-25C-5.  Lend-Lease 
funds financed contracts signed on January 23, 1942 for 150 NA-94 
(B-25C-10) for Britain and 150 NA-93 (B-25C-15) for China.  However, 
these allotments were not followed in the delivery of actual aircraft.  

The B-25C was outwardly almost identical to the B-25B.  It introduced 
the R-2600-13 Double Cyclone engine with Holley 1685HA carburetors in 
place of the earlier Bendix Stromberg PD-13E-2 units.  The Bendix 
carburetors were favored because of their easier maintenance, but they 
required more careful anti-icing procedures.  De-icer and anti-icing 
systems were added, and a Stewart-Warner cabin heater was added in the 
left wing.  A 24-volt electrical system was also added.  

The armament of the B-25C was the same as that of the B-25B, namely a 
single 0.30-inch machine gun in the nose, two 0.50-inch machine guns 
in the dorsal turret, and two 0.50-inch machine guns in a retractable 
ventral turret.  The ventral turret was often removed in the field.  

The B-25C introduced a new type of tail skid underneath the extreme 
rear fuselage, a solid unit which replaced the spring-loaded tail skid 
of earlier versions.  This type of tail skid was retained throughout 
the Mitchell production run.  

On the earlier B-25s, the exhaust pipe coming out of the back of the 
engines extended all the way to a position underneath the forward 
leading edge of the wing.  On the B-25C, the exhaust pipes were 
considerably shortened, and terminated immediately behind the engines.  

The fuel was carried in four tanks in the inner wing panels, with a 
total capacity of 670 US gallons.  In addition, a 515-gallon tank 
could be installed in the bomb bay for ferrying purposes, bringing 
total fuel capacity to 1255 US gallons.  

Beginning with B-25C serial number 41-12817, a small transparent 
scanning blister was installed above the navigator's station.  At this 
time, the turrets were changed to Bendix Amplidyne type, and a 
carbureter air filter was added.  Changes were made so that an 
additional 304 US gallons of fuel could be carried in auxiliary cells 
in the outer wing panels, for a total of 974 US gallons.  

The B-25C-1 production block introduced under-wing bomb racks which 
could accommodate six to eight 100- to 325-pound bombs.  In addition, 
provisions were made for a rack underneath the fuselage capable of 
carrying a short 22.4-inch torpedo weighing 2000 pounds.  If the 
torpedo was carried, no bombs could be, although a bomb bay fuel tank 
could be used.  The Mitchell was employed only in limited numbers as a 
torpedo plane against Japanese shipping.  However, extensive use was 
made of the external wing racks, which could carry six to eight bombs 
of 100-325 pounds in weight.  

Beginning with the B-25C-5 production block, the 0.30-inch nose gun 
was removed and replaced by a flexible 0.50-inch machine gun in the 
extreme nose and a fixed 0.50-inch machine mounted on the starboard 
side of the nose and firing through a hole cut into the side of the 
Plexiglas glazing.  At the same time, better winterization provision 
were made.  

The B-25C-5 production block also introduced a new type of engine 
exhaust.  The B-25B and earlier C versions had a problem with bright 
spurts of flame being emitted from the exhaust, a dead giveaway during 
night operations.  This problem was so bad that the Mitchell had to be 
restricted from night operations where enemy aircraft could be 
expected.  In these earlier versions, the exhaust from each cylinder 
head was gathered by a collector ring, which directed the exhaust to 
the outside via a single pipe on the side of the nacelle away from the 
fuselage.  Several different exhaust modifications were tried out in 
an attempt to alleviate this problem.  The most effective arrangement 
was found to be a the replacement of the single exhaust pipe by a set 
of "finger"-type flame dampening exhaust collectors which ported the 
exhaust through groups of small rectangular outlets that stuck out 
underneath the trailing edge of the cowl flaps.  These "finger"-type 
flame dampeners were installed on the production line beginning with 
the B-25C-5 production block.  These were fairly effective flame 
quenchers, but they suffered considerable cracking and few B-25Cs 
reached combat zones without the replacement of these finger exhausts 
by full collector rings or by the later Clayton S-shaped stacks that 
were introduced on the -15 production block.  

The B-25C-10 production block introduced an AM remote reading compass, 
provisions for additional cabin heating, and an improved scanning lens 
for the sighting system used by the remotely-controlled ventral
turret.  

Beginning with the B-25C-15 production block, the exhaust collector 
ring was replaced with Clayton "S"-shaped flame dampening stacks 
attached to each individual cylinder.  Cutouts and fairings were added 
to the cowling panels where each of the stacks protruded, creating a 
rather cluttered cowling shape.  These protrusions introduced a slight 
speed penalty, but this was considered an acceptable tradeoff in view 
of the better flame dampening that was achieved.  This feature was 
provided on all subsequent Mitchells.  However, the new exhaust system 
was not all that popular with Mitchell crews, since it resulted in an 
increase in cockpit noise as compared to the old arrangement in which 
collector rings ported the exhaust to the outboard side of the 
nacelles.  

At the same time, emergency hydraulic landing gear lowering devices 
were provided.  

Deliveries on a new contract (NA-96) began in February 1943 with the 
similar B-25C-20.  

Beginning with production block B-25C-25, a "clear-vision" windshield 
was installed.  Provisions were made for the fitting of additional 
fuel tanks for ferrying purposes.  125 gallons of fuel could be 
carried in side-mounted tanks in the waist position.  A 215-gallon 
self-sealing fuel tank could be installed in the bomb bay, and 
provisions for a droppable 335-gallon metal bomb-bay fuel tank were 
made on every second airplane.  

B-25C serial number 43-32732 was fitted with a special bomb bay rack 
to carry an airborne flame thrower.  The results of tests with this 
unusual feature are unknown.  

The first B-25C was accepted in December of 1941, with the 1619th and 
last one being delivered in May of 1943.  

41-12434/13038		North American B-25C Mitchell
				c/n 82-5069/82-5673
41-13039/13296		North American B-25C-1 Mitchell
				c/n 82-5674/82-5931
42-32233/32382		North American B-25C-10 Mitchell
				c/n 94-12641/94-12790
42-32383/32532		North American B-25C-15 Mitchell
				c/n 93-12491/93-12640
42-53332/53493		North American B-25C-5 Mitchell
				c/n 90-11819/90-11980
42-64502/64701		North American B-25C-20 Mitchell
				c/n 96-16381/96-16580
42-64702/64801		North American B-25C-25 Mitchell
				c/n 96-16581/96-16680

Specification of the North American B-25C Mitchell:  

Two Wright R-2600-13 Double Cyclone fourteen-cylinder air-cooled 
radials, each rated at 1700 hp each for takeoff, 1500 hp at 2400 rpm.  
Equipped with Holley 1685HA carburetors.  
Performance:  Maximum speed 284 mph at 15,000 feet.  Cruising speed 
233 mph at 15,000 feet.  Initial climb rate 1100 feet per minute.  An 
altitude of 15,000 feet could be reached in 16.5 minutes.  Service 
ceiling 24,000 feet, Range 1500 miles with 3000 pounds of bombs.  
Weights:  20,300 pounds empty, 34,000 pounds maximum loaded.  
Dimensions:  wingspan 67 feet 67.7 inches, length 53 feet 0 inches, 
height 15 feet 9 inches, wing area 610 square feet.  
Fuel:  The fuel capacity consisted of four tanks in the inner wing 
panels, with a total capacity of 670 US gallons.  In addition, a 
515-gallon tank could be installed in the bomb bay for ferrying 
purposes, bringing total fuel capacity to 1255 US gallons.  Later 
versions had additional auxiliary fuel tanks in the outer wing panels.  
Later versions could also have 125-gallon tanks fitted in side waist 
positions, a 215-gallon self-sealing fuel tank installed in the bomb 
bay, and provisions could be made for a droppable 335-gallon metal 
bomb-bay fuel tank.    
Armament:  Two 0.50-inch machine guns in dorsal turret.  Two 0.50-inch 
machine guns in retractable ventral turret.  One 0.30-inch machine gun 
in flexible mount in the nose.  Starting with B-25C-5 the 0.30-inch 
nose gun was removed and replaced by a flexible 0.50-inch machine gun 
in the extreme nose and a fixed 0.50-inch machine mounted on the 
starboard side of the nose and firing through a hole cut into the side 
of the Plexiglas glazing.  Normal bomb load was 3000 pounds but could 
be increased on the B-25C-1-NA with external underwing racks to a 
maximum of 5200 pounds.  

Sources:

   B-25 Mitchell: The Magnificent Medium, N. L. Avery, Phalanx, 1992.

   Medium with the Mostest--The B-25 Mitchell, Jerry Scutts,
   Air International, Vol. 44, Nos 2 and 3, 1993.

   Boston, Mitchell, and Liberator in Australian Service, Stewart
   Wilson, Aerospace Publications, 1992.

   Famous Bombers of the Second World War, William Green, Doubleday,
   1959.

   North American's Flying Gun--The Story of the B-25 From Paper
   Airplane to Legendary Bomber, Jack Dean, Wings, Vol 23 No 4, 1993.

   United States Military Aircraft Since 1909, Gordon Swanborough
   and Peter M. Bowers, Smithsonian, 1989.

   United States Navy Aircraft Since 1911, Gordon Swanborough and
   Peter M. Bowers, Naval Institute Press, 1990.

   North American B-25A-G Mitchell, Aircraft in Profile, Doubleday, 
   1966.

   Jane's American Fighting Aircraft of the 20th Century, Michael J.
   H. Taylor.

Joe Baugher			  **************************************
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