These weapons, which had been used by the Royal Navy since 1918, had a total weight of 450 pounds, contained the explosive Amatol (with a charge/weight of 75%) and were detonated by a hydrostatically fused pistol. In the early days the minimum depth of detonation was 50 feet. The Mark VII depth-charge was a adaptation fitted with a nose cone and tail unit to provide some ballistic performance when being dropped from an aircraft. Initially these D/Cs were dropped in sticks with intervals of 36 or 60 feet between charges. These weapons, restricted to a maximum release height of 115 feet entered RAF anti-submarine service in 1940. In April 1941 the Mark VIII D/C came into service with a filling of Torpex - 30% more effective than Amatol. Nominally of 250 pounds weight the Mark VIII weighed in at 304 pounds with nose and tail fittings and had a lethal radius of 28 feet against submarines. A small interval between charges resulted in a short stick length which increased the risk of the whole stick under-or overshooting and , on the recommendation of RAF Coastal Commands Operational Research Section, the interval was increased to 100 feet at the end of 1942. At about this time an improved pistol capable of initiating the explosion at a reduced depth of 25 feet came into service, making these weapons more effective against submerging submarines. The depth-charge became the standard weapon of the Allies in the battle against enemy submarines.