Article 11592 of rec.aviation.military:
Xref: ssbunews rec.aviation.military:11592
Newsgroups: rec.aviation.military
Path: ssbunews!not-for-mail
From: jfb@usgp1.ih.att.com (Joe Baugher)
Subject: Bomber Series--North American B-25 Mitchell (13 of 32)
Message-ID: <D31Jxy.E84@ssbunews.ih.att.com>
Summary: B-25G cannon-armed Mitchell
Sender: news@ssbunews.ih.att.com (Netnews Administration)
Nntp-Posting-Host: usgp1.ih.att.com
Reply-To: jfb@uscbu.ih.att.com
Organization: AT&T
Date: Fri, 27 Jan 1995 01:53:58 GMT
Lines: 225

The B-25G (NA-96) was the first version of the Mitchell to introduce 
the 75-mm cannon.  It was intended for anti-shipping strikes in the 
South Pacific.  

In the B-25G, a standard 75-mm Army M4 cannon was mounted to 
fire forward through the nose.  This gun was a revision of the famous 
French 75 of World War I.  The basic concept had been found to be 
feasible with experiments on a converted Douglas B-18A Bolo.  However, 
since the effects of the heavy muzzle blast on the nose structure of 
the Mitchell were unknown, a complete forward fuselage section was 
built and trucked to a secret area in California where firing tests 
could be conducted out of the way of prying eyes.  Guided by these 
tests, the structure was progressively strengthened until full 
resistance to prolonged firing of 75-mm rounds could be demonstrated.  

B-25C-1 serial number 41-13296 was modified as the XB-25G prototype.  
It was fitted with a 75-mm M4 cannon which was 9 feet 6 inches long.  
The bombardier-equipped transparent nose was replaced with a shortened 
armored solid nose that reduced overall length to 51 feet.  The cannon 
was mounted in a cradle in the lower left-hand side of the nose.  The 
cradle extended underneath the pilot's seat and a spring mechanism 
formed part of the gun mounting to take up the 21-inch recoil.  

The modified aircraft made its initial flight on October 2, 1942, test 
pilot Ed Virgin being at the controls and with test engineer Paul 
Brewer being on board.  Because of the additional weight and drag, 
maximum speed fell to 278 mph.  However, flight tests found the stall 
characterists to be normal and diving at speeds of up to 340 mph 
revealed no problems.  

Five more B-25Cs were converted to B-25G standards, and 400 examples 
of the B-25G were built new at Inglewood in -1, -5, and -10 production 
blocks.  58 B-25C-20 and -25 bombers were modified with solid nose, 
two nose guns and 75-mm cannon and were redesignated B-25G.  

Up to the end of the Second World War, the 75-mm cannon of the B-25G 
was the second largest gun fitted to any aircraft, exceeded in size 
only by the 105-mm cannon fitted experimentally to the Piaggio P.108A.  
The firepower of the B-25G's 75-mm cannon has been exceeded in postwar 
years by the 105-mm howitzer carried by the Lockheed AC-130 Spectre 
gunship 

The 75-mm cannon was augmented by two 0.50-inch Browning machine guns 
mounted side-by-side in the nose.  These guns were to be aimed and 
fired by the pilot at the same time as the cannon as anti-flak weapons 
and for ranging purposes in the sighting of the 75-mm cannon.  Both 
the cannon and the nose guns were aimed by a type N-3B optical 
gunsight with a type A-1 combination gun/bomb sight head mounted on 
the pilot's side of the cockpit.  This unit was alse used for minimum 
altitude bombing.  

Rather than incur the extra weight, high cost, and protracted 
development schedule of an autoloader, the 75-mm rounds were manually 
loaded into the cannon by the navigator/cannoneer.  Each shell weighed 
15 pounds, and 21 rounds of 75-mm ammunition could be carried on a 
rack next to the breech of the cannon.  On production aircraft, this 
rack was protected by armor plate on three sides.  

Aft of the nose, the B-25G had the same armament as the B-25C.  The 
upper dorsal turret was retained, but the retractable ventral turret 
was often deleted since hydraulic fluid and dust tended to obscure its 
sighting system.  The lower turret was deleted on the B-25G production 
line effective with serial number 42-65001.  The standard bomb bay was 
retained, but was modified to permit the installation of a standard 
aircraft torpedo.  

The crew of the B-25G was five--pilot, copilot, navigator/cannoneer, 
upper turret gunner, and radio operator.  Since there was no 
bombardier, the pilot fired the nose armament and released the bombs.  
The radio operator also doubled as the ventral turret gunner when this 
turret was fitted.  Additional armor was fitted forward of the 
instrument panel, forward of the loader's station, around the 75-mm 
ammunition rack, and below the windshield.  An external flak plate was 
fitted below the cockpit on the left hand side of the aircraft.  

The first B-25Gs to be delivered to the Southwest Pacific began 
arriving at Brisbane in July of 1943.  The B-25Gs used their heavy 
cannon against flak positions, shipping, and other targets, especially 
during the New Britain campaign in which 1253 rounds of 75-mm cannon 
ammunition were expended in 36 days.  The cannon proved to be an 
effective weapon against barges, freighters and small craft, and a 
single well-placed hit could inflict considerable damage even to a 
destroyer.  However, the muzzle velocity of 1930 feet per second gave 
it a relatively high trajectory, which made accurate range 
determination critical.  In addition, accurate aiming demanded a 
straight run in to the target, increasing vulnerability to enemy fire.  
The cannon was accurate, but it was generally impossible to fire any 
more than four shells in each attack, during which time the Mitchell 
was extremely vulnerable to ground fire since no evasive action could 
be taken.  

B-25Gs were used to a limited extent in the Mediterranean theatre of 
operations, but strong German fighter opposition and much heavier 
anti-aircraft fire tended not to justify the risks to the attacking 
crews.  

The supplementary forward-firing machine gun armament of the B-25G was 
considered to be inadequate, and Major Paul "Pappy" Gunn of "strafer" 
fame strongly recommended adding two more nose guns and providing four 
more guns in blister packs mounted on the fuselage sides.  
Modification to existing B-25Gs were made at the Townsville Field 
Modification Center in Australia, where some of the earlier B-25Cs and 
Ds had been converted for ground strafing.  During field tests, the 
blast during the firing of the blister guns was found to cause 
extensive skin fractures in the adjacent structure.  The fuselage 
structure was reinforced and inspection panels were added to the wing 
center section.  Numerous B-25Gs were also provided in the field with 
a twin 0.50-inch tail turret installed to counterbalance the 
additional weight of the extra 0.50-inch guns mounted in the nose and 
on the e fuselage sides, and a single gun was mounted at the right and 
left waist stations.  

By the time of the Marshalls campaign of early 1944, worthwhile targets 
for the 75-mm cannon had become scarce.  By this time, there were 
fewer targets that could not be dealt with more effectively by machine 
guns or bombs.  Consequently, the big cannon was often removed from 
the B-25G, with a pair of additional 0.50-inch machine guns being 
fitted in the nose tunnel where the cannon had been located.  A total 
of 82 B-25Gs were so modified at the Townsville Depot by April of 
1944.  

Two B-25Gs (FR208 and FR209) were supplied to the Royal Air Force for 
evaluation purposes.  However, they never reached operational service.  

A few B-25Gs reached the Navy as PBJ-1G.  

Specification of the North American B-25G Mitchell:  

Two Wright R-2600-13 Double Cyclone fourteen-cylinder air-cooled 
radials, rated at 1700 hp each for takeoff and 1500 hp at 2400 rpm.  
Equipped with Holley 1685HA carburetors.  
Performance:  Maximum speed 280 mph at 15,000 feet.  
Weights:  19,200 pounds empty, 35,000 pounds maximum loaded.  
Dimensions:  Wingspan 67 feet 6.7 inches, length 50 feet 10 inches, 
height 16 feet 4.2 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:  One 75-mm M4 cannon in nose with 21 rounds.  Two fixed 
0.50-inch machine guns in the nose with 400 rpg.  Two 0.50-inch 
machine guns in top turret, 400 rpg.  Two 0.50-inch machine guns in 
retractable ventral turret, 350 rpg.  This turret was deleted 
effective on B-25G No. 42-65001.  
Normal internal bombload was 3000 pounds.

Serials of B-25G:

42-32383/32532		North American B-25C-15 Mitchell
				c/n 93-12491/93-12640
				32384/32388 modified as B-25G-1
42-64502/64701		North American B-25C-20 Mitchell
				c/n 96-16381/96-16580
				64531 converted to B-25G
				64558 converted to B-25G
				64561 converted to B-25G
				64563 converted to B-25G
				64569 converted to B-25G
				64579/64582 converted to B-25G
				64584/64587 converted to B-25G
				64649 converted to B-25G
				64654 converted to B-25G
				64668 converted to B-25G
				64670/64675 converted to B-25G
				64692 converted to B-25G
				64693 converted to B-25G
				64696/64701 converted to B-25G
42-64702/64801		North American B-25C-25 Mitchell
				c/n 96-16581/96-16680
				64702/64707 converted to B-25G
				64753/64772 converted to B-25G
				64779 converted to B-25G
				64780 converted to B-25G
42-64802/64901		North American B-25G-5 Mitchell
				c/n 96-16681/96-16780
42-64902/65101		North American B-25G-5 Mitchell
				c/n 96-20806/96-21005
				65031 to USN as PBJ-1G 35097
42-65102/65201		North American B-25G-10 Mitchell
				c/n 96-21006/96-21105

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			  **************************************
AT&T Bell Laboratories		  *  "Why are you here, Q?  Have you   *
1000 E. Warrenville Road	  *  been banished from the            *
Room 1N 308			  *  Continuum AGAIN?"                 * 
P. O. Box 3013			  *  	      Capt Jean-Luc Picard     *
Naperville, Illinois 60566-7013	  *              ST-TNG		       *
USA				  **************************************
Phone: (708) 713 4548
jfb@uscbu.ih.att.com
			    Who, me?  Speak for AT&T?  Surely you jest!	


