Two kinds of torpedoes - offensive and defensive - had been devised for use in the Bosphorus. The defensive torpedo consisted of a strong wrought iron tank capable of holding 4 cwt. of gunpowder. The offensive torpedo which was intended for use during a night time attack on an anchored vessel, consisted of a hollow iron pear-shaped vessel filled with gunpowder that could fixed to the end of a 30ft. boom attached to the bow of a steam launch specially built for the purpose.