FN began production in Belgium in 1902. At the start of WWII production moved to Remington in the United States until FN could resume production after the war, actually 1952.
This gun was manufactured in 1937. Because the A5 is the second largest selling automatic shotgun in history (Remington 1100 is #1), there's not much I can say that hasn't already been written.
The Browning A5 has the destinction of being the first mass produced semiautomatic shotgun. John Browning himself called it his greatest achievement at the time, of course that was before the 1911 .45 caliber semiautomatic handgun.
Note: Regarding the Serial Number Table, the pre-WWII guns in this serial number range have markings as pictured above. I also have a very low numbered 16 gauge that was made in the first 20 years of production, see that page for a comparison.