Umbra attacked the German steamer Silberg off Tunisia in December 1942 while it carried ammunition, stores, artillery, and vehicles for Axis forces. The resulting explosion destroyed the ship and appeared to leave only two of the three escorting aircraft. The aircraft had been at least 1,000 feet above the sea, and Umbra observed no further evidence of what happened to the missing aircraft. An aircraft loss caused by the blast remains possible, although the limited reports make that explanation seem unlikely. Umbra nevertheless returned to port with an aircraft symbol on her Jolly Roger.
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HMS Umbra and the possible torpedoed aircraft
Umbra's destruction of the ammunition-laden Silberg left an escorting aircraft unaccounted for, creating a possible but unlikely claim that a torpedo had also brought down an aircraft.