On 7 March 1940 Nazi Germany's Kriegsmarine requisitioned her to carry troops and equipment before Operation Weserübung, the invasion of Norway and Denmark, began on 9 April 1940.

[4] The secret plan for the ship was to arrive at Bergen immediately after German troops had captured the city.

The Polish submarine commander, Lieutenant Jan Grudziński, then ordered the ship to surrender or be sunk, but Rio de Janeiro did not reply.

Grudziński informed the British Admiralty about the sinking of this northbound transport ship with German troops.

At 12.00, an aircraft from the Royal Norwegian Navy Air Service started circling around the sinking ship.

The facts that there were horses aboard and that many of the dead and survivors were wearing military uniforms caused an alert to the central authorities.

In June 2015, more than 75 years after the torpedoing, the wreck was finally located by a Norwegian diving company at about 135 metres (443 ft) depth off Lillesand.