The Ithaca 37 was made from patents by J M Browning,our greatest firearms designer. He died in 1927, but his weapons still keep being made, from the 1911 to the Browning 50.
The Ithaca is one great shotgun. the design doesn't lend itself to extended mags, other wise it's as good a design as any now made, and better than most.
BTW, never saw one in Nam, saw plenty of Model 12 and 97 Winchesters, A-5s, 870s and Savages.