Ok, so why has this gotten so out of control?
A simple search concludes that Singer US DID manufacture M1 Carbine receivers, along with a whole poo-pot fun of other stuff.
It appears that Singer was an extremely important part of the war effort.
Here's the scoop in what the Singer US plant did during the war (includes source document reference for the skeptics...):
Singer's Role in WWII
Prior to WWII, employment at the Elizabethport, N.J. Singer factory totaled 5,000. The 113 acre factory comprised 48 buildings with a combined floor area of over 2.6 million square feet. The self-sufficient plant included a foundry, wire drawing mill, hardening and tempering facilities, as well as machining and press operations. The factory produced its own nuts, bolts, springs and pins, tools, gauges and fixtures and contained a photographic and printing plant as well as metallurgical and chemical laboratories for the testing materials.
Increased demands for family sewing machines, repair parts and needles began to be felt in late 1939. The Singer factory in Scotland was engaged in the war effort and shipping throughout Europe was limited which resulted in Singer sales outlets normally supplied from Scotland turning to Elizabethport for family sewing machines and machine parts. By 1940, France had fallen and England was on the verge of collapse. Demand on Elizabethport was further increased by sales outlets attempting to build stock in anticipation of the United States becoming involved in the war. Through 1941 Elizabethport met the demands for family sewing machines, parts, and needles and increased their volume of war work and industrial sewing machine production.
During this period the use of materials such as copper, iron, steel, and aluminum became critical and production of civilian goods such as family sewing machines was completely stopped by order of the War Production Board. The order stopping family sewing machine production—Limitation Order L-98—became effective June 15, 1942. Between that time and July 1945 production of family sewing machines at Elizabethport was completely stopped and only limited production of repair parts and needles was allowed by War Production Board regulations. The halt of the supply of family sewing machines to sales outlets for a period of over three years presented a critical problem to the sales organizations. In addition to the stoppage of family sewing machine production, the board ordered the majority of existing stock of completed family sewing machines frozen and earmarked for use by government agencies. Releases of frozen stock were authorized throughout the war, most to South American countries in promotion of the National Good Neighbor Policy.
Elizabethport personnel who were released from working on family sewing machines due to Limitation Order L-98 were absorbed into the factory's war production effort. Singer's American factories were responsible for the development and production of a variety of items for the war effort including:
.45 caliber automatic pistols
M5 Director equipment to control the fire of 37mm and 40mm anti-aircraft guns
B-29 gunfire control computers
Hydraulic servo assemblies
Subassemblies for the M7 Director 90mm anti-aircraft gun
Gun turret castings for the B-29 bomber
Castings for aircraft engine piston rings
Gun sights for the Mark XV 3-inch, 5-inch, and 40mm anti-aircraft guns on naval ships
Caliber .30 M1 carbine receiver
Director M5 parts
Parts for the Sperry Directional Gyro and Artificial Horizon instruments
Housings and covers for the A3 Automatic Pilot
Parts for the T-1 bomb sight
Ammunition boxes
Time and percussion fuses
Variable pitch wooden propeller blades
Special types of motors for fire control and other ordnance equipment
As a way to acknowledge the importance of the industrial workers to the war effort, the Army-Navy Production Award "E" Pennant was created. Awarded to a plant rather than a company, it consisted of a flag to be flown over the plant and a lapel pin for every employee within the plant. In November 1942 Singer's Elizabethport, New Jersey plant received the Army-Navy "E" Pennant in recognition of its outstanding production of needed war material. In July 1945, Elizabethport Works was cited for the fifth time, and a fourth star was added to the pennant.
Because of its foundry, tool room, and press and screw machinery, Elizabethport was also able to provide assistance to other manufacturers engaged in the war effort:
Thread milling cutters and motor castings for the Lawrence Aeronautical Corporation
Rumbling barrel castings were made for Springfield Armory
Ball reamers to International Business Machine Company
Surgical instrument forgings were supplied to Brandenburg Instrument Company
Cast iron bars were made for American Gas Accumulator
Thread chasers were supplied to Reliable Machine Screw Company.
Prisms were ground for an optical manufacturer and shafts were ground for Simmonds Aerocessories, Inc.
Parts were oxidized for Taller and Cooper Company, Jersey City
Eight-inch projectiles were sand blasted for Crucible Steel
Stator and rotor plates were heat treated for Allen D. Cardwell
Dental chair castings were produced for S. S. White
Taper pins and spring pins were made in large quantities for Babcock Printing Press, Eastman Kodak, General Electric, Western Electric, Excello Corporation, Submarine Signal Company and Worth Engineering
Thread milling hobs were made for American Type Founders, National Rubber machinery and Webendorfer - all working on 40 mm and 75 mm guns - for *Carl M. Norden, working on bomb sights; for Eisman Magneto Corporation and National Pneumatic, working on gun tubes and shells; also Farand Optical Company, Guilbert and Barker Company, National Broach and Machine Company, Diehl Manufacturing Company, Williams Oil-O-Matic, Miller Printing Machinery and the Dictaphone Corporation, working on a variety of war jobs
Hobs and ground thread taps were produced for Textile Machinery Company, Sperry Instrument Company, Delco Division of General Motors, Teletype Corporation, Ford Motor Company and Maxon, Inc.
* The source Singer in World War II - 1939 to 1945, published in 1946 by Singer Manufacturing Company, lists the name as Carl M. Norden; the correct name is Carl L. Norden, founder of Carl L. Norden, Inc., Manhattan, New York.