Article 10025 of rec.aviation.military:
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From: jfb@usgp1.ih.att.com (Joe Baugher)
Subject: Bomber Series--North American B-25 Mitchell
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Summary: B-25B 
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Date: Sat, 7 Jan 1995 02:34:13 GMT
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Beginning with the 65th Mitchell, the B-25B (NA-62B) version was 
introduced on the production line at Inglewood.  It differed from the 
B-25A primarily in having a much heavier defensive armament, dictated 
by the results of combat reports coming in from Europe.  

The most readily-noticeable difference was the introduction on the 
B-25B of a Bendix L-type power-operated turret installed on the top 
of the rear fuselage which carried a pair of 0.50-inch machine guns.  In 
addition, a pair of 0.50-inch machine guns were mounted in a solid 
Bendix remotely-controlled ventral turret.  This turret could be 
retracted into the belly when not in use, the gun barrels fitting into 
slots in the fuselage when the turret was in the fully up position.  

The retractable ventral turret was generally disliked by the Mitchell 
crews.  The guns were sighted by a complex periscope system of lenses 
and mirrors mounted on the top of the turret's center column.  A 
kneeling gunner aimed the guns by looking through the periscope sight 
eyepiece and directed the guns by operating a dual hand control.  The 
optical sighting system was clumsy and cumbersome for gunners to use.  
Cramped in an awkward kneeling position and peering through the sight, 
the gunner could not see what his hands were doing, and he could not 
see the barrels of his weapons in his sight.  The gunner often became 
dizzy when tracking enemy fighters through the sight, and he sometimes 
got so disoriented and nauseous that he could not even fire his guns.  
In addition, the turret took 55 seconds to be lowered into place and 
set up for firing.  If lowered too quickly, the retracting micro 
switch could be damaged, jamming the turret in the down position and 
creating excessive aerodynamic drag.  In addition, the ventral turret 
often collected mud and dust when operating from unimproved airfields, 
which obscured its sighting system.  The system was usually considered 
more trouble than it was worth, and was generally removed by combat 
units in the field, saving 600 pounds in weight and providing useful 
space for a long-range fuel tank.  

Other armament changes introduced by the B-25B were less apparent.  
The stoable 0.30-inch waist gun of the B-25/B-25A was eliminated, and 
the side hatches with their Plexiglas windows were considerably 
reduced in size.  The B-25B retained the 0.30-inch machine gun in the 
extreme nose that was operated by the bombardier.  However, the 
0.50-inch tailgun was eliminated and the position where the tailgun 
had been located was greatly reduced in size, and became little more 
than a prone observation post, being terminated at its extreme end 
with a transparent cap.  The armor plate in the extreme tail was 
removed.  

The crew was five--pilot, copilot, bombardier/nose gunner, 
navigator/upper turret gunner, and radio operator/belly turret gunner.  
The length was reduced from 54 feet 1 inch on the B-25A to 52 feet 11 
inches on the B-25B.  The additional defensive armament of the B-25B 
caused the the weight to creep up to 20,000 pounds empty and 28,460 
pounds fully loaded, resulting in another degradation in performance.  
Maximum speed was now down to 300 mph at 15,000 feet.  

The first 14 B-25Bs were accepted in August of 1941.  The 17th 
Bombardment group was the first to get the B-25B.  By the time of 
Pearl Harbor on December 7, 1941, North American had delivered 130 
bombers.  With the completion of the last of 120 B-25Bs in January of 
1942, North American met the initial contract for 184 NA-62 aircraft.  

Serials of B-25B:

40-2229/2348		North American B-25B Mitchell
				company numbers 62-2898/62-3017
				2242,2247,2249,2250,2261,2267,2268,2270,2278,
				2282,2283,2292,2297,2298,2302,2344 were 
				Doolittle Tokyo raiders.  2344 was Doolittle's
				plane.
				2243 was cancelled.
				2245, 2255, 2263, 2306, 2309, 2310, and 2316
				were delivered to Brazil
				2347 in storage at Chino, CA.

Specification of North American B-25B Mitchell 

Two Wright R-2600-9 Double Cyclone fourteen-cylinder air-cooled 
radials, each rated at 1700 hp for takeoff and 1500 hp at 2400 rpm.  
Equipped with Bendix Stromberg PD-13E-2 carburetors.  
Performance:  Maximum Speed 300 mph at 15,000 feet.  Service ceiling 
23,500 feet, range 2000 miles with 3000 pounds of bombs.  
Weights:  20,000 pounds empty, 28,460 pounds loaded, 31,000 pounds 
maximum.  
Dimensions:  Wingspan 67 feet 7.7 inches, length 53 feet 0 inches, 
height 15 feet 9 inches, wing area 610 square feet.  
Fuel:  two forward wing tanks, total 368 gallons.  Two rear wing tanks 
total 324 gallons.  One droppable bomb bay tank, 420 gallons.  
Armament:  One 0.30-inch machine gun in flexible mount in the nose.  
Two 0.50-inch machine guns in Bendix dorsal turret.  Two 0.50-inch 
machine guns in retractable Bendix ventral turret.  

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.

   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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