This is an early example of a bell-forward "Sousaphone" tuba.  Shoulder carried bass horns were first seen in the US in the form of bell-backwards "over-the shoulder" instruments common during the US Civil War.  After the war, most brass horns were designed to be bell-forward, or in the case of baritones and tubas, bell up.  Another popular design also evolved called a helicon, which provided a much more easily carried and well balanced tuba with the bell facing off to the left and forward of the musician.  John Philip Sousa is credited with designing the bell-up helicon or "Raincatcher Sousaphone".  This design was supposed to help waft the bass sound over a marching band, but it was still somewhat unwieldy and never gained universal popularity over the helicon, athough the raincatcher and helicon designs were both still being manufactured by Conn into the late 1920s. 

Early in the 20th century, some marching bands directors wished to have the bass sound directed forward - like the higher brass and bell forward trombones, baritones and tenors.  A small modification of the raincatcher design - by adding another 90 degree turn accomplished this objective, and this design has remained popular to this day as the "Sousaphone"!

 This 3 Valve Eb Sousa was made in 1913 (based on the serial number 130866) and has a bell diameter of 17 inches.  It is possible that this was an early transitional design by Conn, who by 1925 was making EEB and BBb Sousaphones with 20-24 inch bells.  I remember carrying a 26" BBb Sousaphone down 5th Avenue in NYC in a St Patrick's Day Parade. The wind whipping down through the skyscrapers would catch that big bell and tried to propel me in the reverse direction!.