Another primitive technique of attacking submarines was the dropping of hand-thrown guncotton bombs. The Lance Bomb was developed, also; this featured a cone-shaped steel drum on a shaft, intended to be thrown at a submarine. Firing Lyddite shells, or using trench mortars, was tried. Use of nets to ensnare U-boats was also examined, as was a destroyer, , fitted with a spar torpedo. To attack at set depths, aircraft bombs were attached to lanyards which would trigger their charges; a similar idea was a guncotton charge in a lanyarded can; two of these lashed together became known as the Depth Charge Type A. Problems with the lanyards tangling and failing to function led to the development of a chemical pellet trigger as the Type B. These were effective at a distance of around .