Date: 1920's. Owner unknown
The 26L was produced from about 1928 through at least 1930. It was pitched in Bb with an extra slide for G-F.
What Conn said in 1930:
The Legionnaire Three-in-one Trumpet is a new model built in Bb with extra slide to G and F. It is destined to be a leader in the long model bugle field. A corps equipped with these bugles will have an advatage over other corps because of the striking appearance and marvelous tone of these instruments. [It] balance[s] perfectly from the finger hook hold. [It is] extremely easy to blow and [is] absolutely true in pitch. The long model bugles make it possible to attach tabards to every bugle in the corps.