On Two Fronts    One Million Browning Machine Guns
AC Spark Plug Division of GMC in World War Two
Flint, MI
1908-1988
Rest in Peace

This page updated 4-19-2021.

The signature product of the AC Spark Plug Division of General Motors during WWII was aircraft spark plugs.  While AC Spark Plug made a wide variety of goods for the military during WWII, it made millions of aircraft spark plugs, as both aircraft production and air combat missions increased.  Demand was so great that AC Spark Plug set up spark plug manufacture in a borrowed Fisher Body plant in Ionia, MI.  Author's photo from the Michigan Military Technical and Historical Society.

  Of the 295,959 aircraft built by American manufacturers during World War Two, 7,546 were TBM torpedo bombers constructed by the Eastern Aircraft Division of General Motors at Trenton, NJ.  The TBM was powered by a Wright R-2600 radial engine with fourteen cylinders, each with two spark plugs.  After a navy squadron of twelve TBMs returned from a combat mission, all of the spark plugs were replaced.  Even though there were two sparkplugs per cylinder, no pilot wanted a cylinder to start missing over the water, or when full power was needed in combat.  This was common practice throughout the war by all aviation combat units.  Aviation spark plugs were consumed at a prestigious rate during the war!  Author's photo from the Liberty Aviation Museum in Port Clinton, OH.

Pages 4 and 16 of "On Two Fronts" note that AC Spark Plug built torpedo directors which were used in the Battle of Midway.  This very rare example of the AC Spark Plug-built torpedo director is also on display at the Michigan Military Technical and Historical Society.  Author's photo added 4-19-2021.

Author's photo added 4-19-2021.

Author's photo added 4-19-2021.

AC Spark Plug Division of General Motors World War Two Products:  Air Cleaners, Air Cleaner Replacement Elements, Aircraft Coolant Pressure Relief Valves, Sperry Automatic Pilots, Bombsights, Cable Terminal Connectors, Carbon Stack Insulators, Carburetor Intake Silencers and Air Cleaners, Crankcase Breathers, Crankcase Ventilating Valves, Die Castings, Diesel Engine Intake Silencers, Electric Pressure and Vacuum Pumps, Engine Bearings for Aircraft, Tanks, and Trucks, Firing Pins for Anti-Aircraft Shells (Should this be for Anti-Aircraft Guns?), Flame Arrestors, Flexible Shafts and Cables, Fuel Pumps -Electrical and Mechanical, Fuel and Vacuum Pumps, Fuel Pump Repair Kits, Gas Tank Pressure Caps, Gasoline Strainers, Ignition Cable Terminals, Instrument Panels for Tanks, Armored Cars, Trucks, and Marine Craft, (containing:  Ammeters, Fuel Gauges, Indicator Lights, Oil Indicator Switches, Oil Pressure Gauges, Speedometers, Tachometers, Water Temperature Gauges, Voltmeters), Machine Guns - Browning .50 Caliber, Oil Filters - Lubricating and Fuel, Oil Filter Replacement Elements, Oil Temperature Gauges, Oxygen Pressure Gauges, Radiator Pressure Caps, Shell Magazines, Spark Plugs - Automotive and Aircraft, Spark Plug Cleaners, Spark Plug Gaping Tools, Speedometers Drive Adaptors, and Torpedo Directors.

Early Product Development at AC Spark Plug:  The name of the division is AC Spark Plug, but it is obvious from the above that it made more than spark plugs.  In 1919 AC Spark Plug added speedometers to its product line.  In 1925 it added air cleaners, and in 1926 oil filters and gas filters started coming off its assembly lines.  These were followed in 1927 by mechanical fuel pumps, ammeters, oil and temperature gauges, and tachometers.  In 1928 the division began the manufacture of complete instrument panels and crankcase breathers.  Fast forward to 1975 and past many other new products, and AC Spark Plug Division began producing the catalytic converters that were installed on all General Motors passenger cars and some light trucks.  New products were introduced during its entire life cycle.  AC Spark Plug was just more than a spark plug manufacturer. 

Author's Note:  The above list comes from the October 1943 AC Spark Plug publication "On Two Fronts."  There was almost two years left of World War Two.   AC Spark Plug manufactured other products not listed above because they were developed as the war progressed.  One such example is the K-14 Gun Sight documented below.

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The AC Sparkplug Division of General Motors Flint, MI won the Army-Navy "E" Award five times.  The original award was presented on September 2, 1942, and the first star was added in June 1943.  The dates of the remaining three stars are unknown.

The AC Spark Plug Division of General Motors Ionia, MI Plant won the Army-Navy "E" Award two times.  This was a Fisher Body Plant loaned to AC for the manufacture of spark plugs.


The original "E" flag at AC Spark Plug in Flint, MI.

This 12x8 foot sign was built into the overpass at the original AC Spark Plug plant on Industrial Avenue in 1909.  Currently it is on display at the Sloan Museum in Flint, MI after being donated to the museum by General Motors.  Author's photo.

Author's photo.

This is the original Champion spark plug plant on the southeast corner of Industrial Avenue and Harriet Street in Flint, MI after the addition of 18,000 square feet in 1915.  Champion came to Flint in 1908 at the request of Billy Durant, to supply spark plugs to the fledgling local auto industry.  Originally, Champion was located in a Buick building, but then built the one shown above in 1912.

The Industrial Avenue plant as originally built was 33,000 square feet.  The addition of a second building at the site in 1915 added 18,000 square feet.  In 1918 more buildings were added bringing the total square footage to 88,000 square feet. 

This photo shows the AC Spark Plug plant on Industrial Avenue, at a later date after much expansion.  The original structure is in the center portion on the left-hand side or west side of the photo.  Expansions were built to the north and south of the original structure, and also on the east side of Industrial Avenue.  During World War Two this was AC Spark Plug's main manufacturing plant.  Many of the products it supplied for the war effort were built here.  In 1975 it was closed and then razed.

This is an early photo of the AC Spark Plug plant on Dort Highway.  J. Dallas Dort originally built the plant in 1915 built to produce automobiles.  AC Spark Plug purchased the plant in 1925 after the Dort Motor Company went out of business in 1924, and before becoming part of General Motors in 1929.

The Dort Highway plant looking northeast from across Dort Highway.

Auto-pilots and Bombsights:  During World War Two, Sperry Corporation was a producer of bomb sights and auto-pilots for military aircraft.  With the attack on Pearl Harbor in December 1941, the demand for these products exceeded the capability of Sperry to provide them.  At the request of the U.S. government, AC Spark Plug took on the task of also building Sperry auto-pilots and bombsights for American aircraft.  Below are several of the Sperry components AC Spark Plug built during WWII.  More information on these products can be found in "On Two Fronts" published by AC Spark Plug in October 1943.  There are links to this publication at the top and bottom of this page.

On display at the Sloan Museum in Flint, MI is a AC Spark Plug built auto-pilot on the left, and a mechanical analog bombsight computer on the right.  Author's photo.


Author's photo.


Author's photo.

The data plate on the bombsight computer indicates it is the vertical gyro part number 644841, and was built under license by AC Spark Plug.  Author's photo.

Author's photo.

This AC Spark Plug Division-built Sperry vertical gyro is on display at the Tri-State Warbird Museum in Batavia, OH.  The cover has been lifted to show the internal workings of the unit.  Author's photo.

The gyroscope can be at the rear of the unit.  Author's photo.

Author's photo.

The component on the left of the display is the vertical gyro for the Sperry auto-pilot.  Author's photo.

The direction gyro is part number 656029.  Author's photo.

This Sperry T-1-A bombsight computer was built by A-C Sparkplug and was used with the sighting head also shown.  It was photographed as part of the special International Radio Corporation/Argus display at the Yankee Air Museum in Belleview, MI.  Author's photo added 2-10-2019.

Author's photo added 2-10-2019.

Author's photo added 2-10-2019.

This T-1-A Bombsight Computer was built in 1943 and is Serial Number 43-19718.  Author's photo added 2-10-2019.

Author's photo added 2-10-2019.

 On display at the Michigan Military Technical and Historical Society is this Sperry A-5 auto-pilot amplifier that was supposed to be installed in Ford built B-24.  Unfortunately it did not meet the requirements of the Ford incoming inspection, and was rejected.  On the positive side, if it had not been rejected, it would not have been saved for eventual display at the museum.  Author's photo

AC Spark Plug was not a subsidiary of General Motors.  It was a Division of GM. 

This Sperry A-5 Pilot's Turn Control was also built by A-C Sparkplug.  It was photographed as part of the special International Radio Corporation/Argus display at the Yankee Air Museum in Belleview, MI.  Author's photo added 2-10-2019.

Author's photo added 2-10-2019.

Author's photo added 2-10-2019.

This Sperry A-5 Navigator's Turn Control was also on display as part of the special International Radio Corporation/Argus display at the Yankee Air Museum in Belleview, MI.  Author's photo added 2-10-2019.

Author's photo added 2-10-2019.

A B-24 like the ones Ford built at Willow Run, MI.  The B-24 was also built in California, Oklahoma, and Texas.  AC Spark Plug built Sperry components may have also been shipped to these locations.  Author's photo.

"On Two Fronts" discusses AC Spark Plug building a bombsight.  But it is very generic and does not state much else because bombsights during World War Two were top secret devices.  There were two advanced bombsights used by the United States military;  the Norden and the Sperry.  While the Norden was the most famous, and the better of the two bombsights, the Sperry was also used in many bombers during the war.  From what "On Two Fronts" says, it was also given to American allies during the war.  The Norden was only used by American bombers.  AC Spark Plug no doubt built the Sperry version, due to its relationship with the company.  This one was photographed by the author at the National Museum of the United States Air Force in Dayton, OH.

Author's photo.

K-14 Series Gun Sights:  AC Spark Plug Division was the sole supplier of K-14s gyro-computing gun sights during WWII.  These sights were a post-1943 development, and not included in the October 1943 "On Two Fronts."  The Division produced the A, B and C models of the K-14.  The K-14B series gun sights were introduced in September 1944 for P-51D Mustang fighters, making K-14B the most modern of the gun sights utilized by the US Army Air Forces in WWII.  K-14B gun sights were used on American fighters up through the 1950s, even on some early jet aircraft.  It was the ultimate in World War Two American gun sights.

Bendix made the naval version of the K-14 during World War Two.  After the war Eastman Kodak in Rochester, NY continued the production or remanufactured the K-14 series for the early post war period.

Below is an AC Spark Plug manufactured K-14B on display at the Sloan Museum in Flint, MI.

Author's photo.

Author's photo.

Author's photo.

K-14B Gun Sight at the Cradle of Aviation Museum on Long Island, NY, May 2018:

Walking up to this display at the Cradle of Aviation Museum and understanding immediately that I had found a precious piece of AC Spark Plug history in New York, would not have been possible without my trip to the Sloan Museum two months earlier in March.  Previously, I was totally unaware that AC Spark Plug made gun sights for fighter aircraft in World War Two.  Without the knowledge gained in March, I would have walked right by this display, not knowing that the K-14B Gun Sight was used on late model P-47s. 

This P-47 instrument panel on display at the Cradle of Aviation Museum on Long Island, NY has an AC Spark Plug built K-14B Gun Sight on it.  Author's photo added 8-4-2018.

Author's photo added 8-4-2018.

Author's photo added 8-4-2018.

Author's photo added 8-4-2018.

Author's photo added 8-4-2018.

Author's photo added 8-4-2018.

Author's photo added 8-4-2018.

The Republic P-47 Thunderbolt utilized the K-14B gun sight after September 1944.  Author's photo added 8-4-2018.

The  P-51D also utilized the K-14B gun sight after September 1944.  Author's photo.

Oxygen Flow Indicator (Blinker):  "On Two Fronts" describes how AC Spark Plug developed the Oxygen Blinker; and shows the engineering capability of AC Spark Plug during World War Two to develop products beyond the normal automotive product line.  This was a very important instrument for bomber crews to verify that oxygen was flowing at high altitudes.  AC Spark Plug did not have the manufacturing capacity to make the Blinker, so Delco Radio built the instruments during the war.

  At altitudes above 10,000 feet, aircrews in World War Two needed supplemental oxygen to stay alive, as the oxygen content thinned out.  Each crew member on an aircraft would have one of these indicators which blinked when oxygen was flowing.  It was an important visual aide, allowing a crewman to quickly verify that his all-important oxygen was flowing.  Author's photo.

This view, from the bombardier's position on a B-17 undergoing restoration, shows how the AC Spark Plug designed Blinker was part of the crew member's entire oxygen system.  AC Spark Plug produced oxygen pressure gauges like the one to the right of the Blinker, and were used in many of the American military aircraft of World War Two.  Author's photo from the Champaign Aviation Museum in Urbana, OH.
 

.50 Caliber Machine Gun:  The .50 caliber heavy machine gun was AC Spark Plugs' signature WWII product.  On September 30, 1940, AC Spark Plug received an order for 14,741 aircraft flexible and 7,385 heavy barrel .50 caliber machine guns.  By November 1944, AC and three other GM divisions had produced one million machine guns.  Between Saginaw Steering Gear and Frigidaire Divisions of GM, they produced 775,384 Browning machine guns by war's end.  The amount that Brown-Lipe-Chapin built is unknown but estimated at 100,000.  An estimate for the number of .50 caliber Browning machine guns built by AC Spark Plug is 250,000.

The complete story of AC Spark Plug's manufacture of .50 caliber machine guns is explained in detail in both "On Two Fronts" and "One Million Browning Machine Guns."  There are links to these two documents at the top and bottom of this page.

This cut-away of .50 caliber Browning machine gun was found in the maintenance shop of the National Armor and Cavalry Museum at Fort Benning, GA.  Author's photo added 10-7-2018.

Author's photo added 10-7-2018.

Author's photo added 10-7-2018.

The .50 caliber heavy barrel machine gun was used by all of the services in WWII.  Author's photo.

Author's photo.

Author's photo.

Instrument Panels:  According to page 26 of "On Two Fronts," written in October 1943, AC Spark Plug had 15 different types of instrument panels that were used in tanks, trucks, submarines, jeeps, and small boats.  As the war progressed, new weapons were introduced that required more and different instrument panels.  This was especially true for armored vehicles, which included the Buick built M18 Hellcat tank destroyer, Cadillac built M26 Chaffee light tank, and the Fisher Body M26 Pershing heavy tank.

This photo from "On Two Fronts" shows an instrument panel that would go into a M4A2 Sherman tank, or an M10 Wolverine tank destroyer.  Both were powered by twin Detroit Diesel engines requiring two sets of instruments and switches to operate the vehicles. 

"On Two Fronts" states that AC Spark Plug instrument panels were used in all Sherman tanks.  If so, the GM Division supplied 49,234 instrument panels for five different types of Sherman tanks built by ten different companies from the State of Washington to Pennsylvania.

One thing is certain.  AC Spark Plug supplied instrument panels and other components to other General Motors Divisions that were building tanks, tank destroyers, and armored cars.  The Fisher Body Tank Arsenal in Grand Blanc, MI was just 5.5 miles south of the main AC Spark Plug plant on Industrial Ave. in Flint.  During WWII the Grand Blanc Tank Arsenal turned out 19,034 tanks and tank destroyers with AC Spark Plug components in them.

This M4A2 is the oldest Fisher Body built tank in on display in North America.  It is located at Victoria Park in London, Ontario.  It came off the Grand Blanc assembly line in September 1942 with AC Spark Plug parts.  It landed with the Canadian Army at Normandy, and then fought its way across Europe until the end of the war.  It survived its many battles, and then came back to Canada.  Fisher Body Grand Blanc produced 7,508 M4A2 Sherman tanks.  Author's Photo.

This is a cutaway of a Fisher Body Grand Blanc M4A2 on display at the Canadian War Museum in Ottawa, ONT.  Author's Photo.

The AC Spark Plug instrument panel.  Author's Photo.

Author's Photo.

The M4A2 was powered by two Detroit Diesel 6-71 engines.  Author's Photo.

Four of the six AC Spark Plug air filters can be seen in this photo along with a cutaway of one oil filter.  Author's Photo.

The Grand Blanc built M10 Wolverine tank destroyer had the same power train as the M4A2.  4,993 were built at Grand Blanc.  Author's Photo.

Of all of the Sherman Tanks built during WWII, it is noteworthy that a Fisher Body M4A3(75) tank built in Grand Blanc, MI has the honor of representing all of the M4s that participated in the Battle of the Bulge.  Registration Number 3081532 was one of 339 M4A3 Sherman tanks built in the Fisher Body Tank Arsenal in Grand Blanc, MI in March 1944.  It has an AC Spark Plug instrument panel.  The engine is a Ford built 500 hp V-8 which would have Ford components in the engine bay.  Author's photo.

Buick was located near AC's main plant on Industrial Avenue.  Buick built 2,507 M18 Hellcats with AC Spark Plug instrument panels installed.  Author's photo.

"On Two Fronts" states that AC Spark Plug instrument panels were used in all M5 and M5A1 Stuart light tanks.  If so, then, AC Spark Plug supplied instrument panels for 6,810 M5 series tanks built by the Cadillac and Southern California Divisions of GM, and Massey Harris.  Each tank had two Cadillac V-8 engines that would have AC air, fuel, and oil filters.

This Cadillac built M5 came off the assembly line in September 1942.  Author's photo from the First Division Museum in Wheaton, IL.

After M5 production halted, Cadillac and Massy Harris built 4,731 M24 Chaffee light tanks powered by twin Cadillac V-8 engines equipped with AC Spark Plug components.  Author's photo from the First Division Museum in Wheaton, IL.

Fisher Body and Chrysler built 2,202 M26 Pershing heavy tanks in 1944 and 1945.  Each one had an instrument panel built by AC Spark Plug.  This particular Fisher Body M26 was at the Battle for the Remagen Bridge on the Rhine River in March 1945.  Author's photo from the Wright Museum of WWII in Wolfeboro, NH.

Chevrolet was also located near AC's main plant on Industrial Avenue.  Chevrolet built 3,844 Staghound armored cars for the United Kingdom.  Along with the AC instrument panels, the division also supplied the fuel, air and oil filters for the two GMC 6-cylinder engines that powered the Staghound.  Author's photo from the Canadian War Museum in Ottawa, ONT. 

GMC and Chevrolet built 528,829 2-1/2 ton 6x6 trucks with the GMC nameplate on it.  Author's photo.

Seen here is one of the 528,829 AC Spark Plug instrument panels that were installed in the GMC trucks.  AC Spark Plug also supplied 528,829 oil, air, and fuel filters for the GMC inline six engines.  Author's photo.

GMC and Chevrolet built 21,147 2-1/2 ton 6x6 amphibious trucks DUKWs with the GMC nameplate on it. Author's photo.

It was built with AC instrument panels, and oil, air, and fuel filters.  Author's photo.

"On Two Fronts" mentions instrument panels used in submarines.  This panel was for the four engines built by Cleveland Diesel Division of GM, which powered 136 American submarines during WWII.  This is the USS Cod in Cleveland, OH.  Author's photo.

Below are links to "On Two Fronts" and "One Million Browning Machine Guns."  Both give excellent detail on operations at AC Spark Plug during WWII.

 
On Two Fronts

One Million Browning Machine Guns