[1] Fenian Ram's design was partly modelled on the Whitehead torpedo, and it had similar cruciform control fins near the tail.

The boat did not simply take on ballast until she sank like other contemporary submarines; she maintained a slightly positive buoyancy, and tilted her horizontal planes so that her forward motion forced her under.

Fenian Ram was armed with a 9-inch (229 mm) pneumatic gun some 11 feet (3.4 m) long, mounted along the boat's centerline and firing forward out of her bow.

To reload, the outer door was again shut and the water in the tube was blown into the surrounding ballast tank by more compressed air.

In 1916, Fenian Ram was exhibited in Madison Square Garden to raise funds for victims of the Easter Rising.