Bass cavalry valve trombone. Nominal pitch: B♭|+|F.

https://images.is.ed.ac.uk/luna/servlet/iiif/UoEart~2~2~78193~183452/full/150,/0/default.jpghttps://images.is.ed.ac.uk/luna/servlet/iiif/UoEart~2~2~78526~183451/full/,150/0/default.jpg