Expanding bowie knife / dagger.

In the closed position it is 11-3/8 inches (29 cm) long, with the blade being 5-1/2 inches (14 cm) long.
In the open position the overall length is 15-5/8 inches (40 cm) and the blade length is 10 inches (25.4 cm).

The front bolster (or ferrule) rotates and locks the blade in the open position similar to the French Opinel.
The back bolster (or ferrule) rotates to lock the blade closed.
[See the 1891 US Patent below.]

Halfway down the blade is stamped: GESETZL. GESCHUTZT and underneath this is No 354.
GESETZLICH GESCHUTZT is German for Legally Registered (similar to Design Patent).

The tang is stamped QUALITAT / I ^A.

Both of the bolsters are nickel silver and impressed with a shield bordered on each side by two whales that are head to head.
On the shield is, GESETZLICH (on top) GESCHUTZT (on the bottom). In between is an anchor.

The center part of the handle is very dark wood, almost black.

The sheath was custom made to fit the knife when folded, but it is considerably newer than the knife.
It was made by the Herman H Heiser Saddlery Company of Denver, Colorado, probably in the 1940s.