Question: Northwest Outpost starred what American singer who appeared in 19 musical films in the 1930s and 1940s?

Context articles: Walter Cassel
Dick Williams (singer)
Northwest Outpost
Deanna Durbin
Kenneth Lee Spencer
Robert B. Sherman
Shirley Jones
Nelson Eddy
Richard M. Sherman
Jeanette MacDonald

Walter Cassel (May 15, 1910 – July 3, 2000) was a renowned American operatic baritone and actor.
 He began his career singing on the radio during the mid-1930s and appeared in a couple of Hollywood musical films in the late 1930s.
 He made his first stage appearances in a handful of Broadway productions during the late 1930s and early 1940s.
 He began his opera career at the Metropolitan Opera in 1942, and went on to have a long and fruitful association with that house that lasted until his retirement from the stage in 1974.
 In addition to working with the Met, Cassel was also a regular performer with the New York City Opera between 1948 and 1954 and worked frequently as a freelance artist with important opera companies on the international stage as well as in the United States.
Dick Williams (born June 7, 1926) is an American singer and actor.
 He is the older brother of Andy Williams and had started out like Andy in The Williams Brothers.
 Williams was born in Wall Lake, Iowa, the son of Jay Emerson and Florence (née Finley) Williams.
 While living in Cheviot, Ohio, Williams attended Western Hills High School in Cincinnati, Ohio.
 He finished high school at University High School, in West Los Angeles, because of his family's move to California.
 Williams had brothers: Bob, Don, and Andy.
 One of his first performance was in a children's choir at the local Presbyterian church.
 He and his brothers formed the Williams Brothers quartet in late 1938, and they performed on radio in the Midwest, first at WHO, in Des Moines, Iowa, In July 1940 the family the family moved to Chicago and received a job at WLS, in Chicago, and WLW, in Cincinnati.
 Moving to Los Angeles in 1943, the Williams Brothers sang with Bing Crosby on the hit record "Swinging on a Star" (1944).
 They appeared in four musical films: "Janie" (1944), "Kansas City Kitty" (1944), "Something in the Wind" (1947) and "Ladies' Man" (1947).
The Williams Brothers were signed by Metro-Goldwyn-Mayer to appear in "Anchors Aweigh" and "Ziegfeld Follies" (1945) but, before they went before the cameras, the oldest brother, Bob, was drafted into military service and the group's contract was canceled.
 Kay Thompson, a former radio star who was now head of the vocal department at MGM, had a nose for talent and hired the remaining three Williams brothers to sing in her large choir on many soundtracks for MGM films, including "The Harvey Girls" (1946).
 When Bob completed his military service, Kay hired all four brothers to sing on the soundtrack to "Good News" (1947).
Northwest Outpost (also known as End of the Rainbow) is a 1947 American musical film directed by Allan Dwan and starring Nelson Eddy, Ilona Massey and Joseph Schildkraut.
 The film was Eddy's last, and is an operetta film like his previous starring roles.
 He was persuaded to make it by Republic Pictures because Rudolf Friml was writing the score.
 It was well received by critics and had a strong box office performance.
Edna Mae Durbin (December 4, 1921 – April 20, 2013), known professionally as Deanna Durbin, was a Canadian actress and singer, who appeared in musical films in the 1930s and 1940s.
 With the technical skill and vocal range of a legitimate lyric soprano, she performed many styles from popular standards to operatic arias.
Kenneth Lee Spencer (25 April 1913 - 25 February 1964), usually known as Kenneth Spencer, was an African-American opera singer and actor.
 A talented bass-baritone, Spencer starred in a few Broadway musicals and musical films in the United States during the 1940s.
 Frustrated with the racial prejudice he experienced in the United States, Spencer moved to West Germany in 1950 where he had a successful opera and concert career.
 He also appeared in a number of German films.
 His career was cut short when he died in the crash of Eastern Air Lines Flight 304.
Robert Bernard Sherman (December 19, 1925 – March 6, 2012) was an American songwriter who specialized in musical films with his brother Richard Morton Sherman.
 According to the official Walt Disney Company website and independent fact checkers, "the Sherman Brothers were responsible for more motion picture musical song scores than any other songwriting team in film history."
 Some of the Sherman Brothers' best known songs were incorporated into live action and animation musical films including: "Mary Poppins", "The Jungle Book", "The Many Adventures of Winnie the Pooh", "Chitty Chitty Bang Bang", "The Slipper and the Rose", and "Charlotte's Web".
 Their most well known work, however, remains the theme park song "It's a Small World (After All)".
 According to Time.com, this song is the most performed song of all time.
Shirley Mae Jones (born March 31, 1934) is an American singer and actress of stage, film and television.
 In her six decades of show business, she has starred as wholesome characters in a number of well-known musical films, such as "Oklahoma!
" (1955), "Carousel" (1956), and "The Music Man" (1962).
 She won the Academy Award for Best Supporting Actress for playing a vengeful prostitute in "Elmer Gantry" (1960).
 She played the lead role of Shirley Partridge, the widowed mother of five children, in the musical situation-comedy television series "The Partridge Family" (1970–74), which co-starred her real-life stepson David Cassidy, son of Jack Cassidy.
Nelson Ackerman Eddy (June 29, 1901 – March 6, 1967) was an American singer and actor who appeared in 19 musical films during the 1930s and 1940s, as well as in opera and on the concert stage, radio, television, and in nightclubs.
 A classically trained baritone, he is best remembered for the eight films in which he costarred with soprano Jeanette MacDonald.
 He was one of the first "crossover" stars, a superstar appealing both to shrieking bobby soxers and opera purists, and in his heyday, he was the highest paid singer in the world.
Richard Morton Sherman (born June 12, 1928) is an American songwriter who specialized in musical films with his brother Robert Bernard Sherman.
 According to the official Walt Disney Company website and independent fact checkers, "the Sherman Brothers were responsible for more motion picture musical song scores than any other songwriting team in film history."
 Some of the Sherman Brothers' best known songs were incorporated into live action and animation musical films including: "Mary Poppins", "The Jungle Book", "The Many Adventures of Winnie the Pooh", "Chitty Chitty Bang Bang", "Snoopy Come Home", "Bedknobs and Broomsticks", "The Slipper and the Rose", and "Charlotte's Web".
 Their most well known work, however, remains the theme park song "It's a Small World (After All)".
 According to Time.com, this song is the most performed song of all time.
Jeanette Anna MacDonald (June 18, 1903 – January 14, 1965) was an American singer and actress best remembered for her musical films of the 1930s with Maurice Chevalier ("The Love Parade", "Love Me Tonight", "The Merry Widow" and "One Hour With You") and Nelson Eddy ("Naughty Marietta", "Rose-Marie", and "Maytime").
 During the 1930s and 1940s she starred in 29 feature films, four nominated for Best Picture Oscars ("The Love Parade", "One Hour with You", "Naughty Marietta" and "San Francisco"), and recorded extensively, earning three gold records.
 She later appeared in opera, concerts, radio, and television.
 MacDonald was one of the most influential sopranos of the 20th century, introducing opera to movie-going audiences and inspiring a generation of singers.