During this period, the general explosive used in torpedo warheads was TNT.
For ordinary bombs or shells, TNT was sufficient and did not require improvement. In fact, TNT was quite advanced for its time.
(Note: TNT began to be used as an explosive around 1907. Before that, picric acid was used. TNT was mainly used as a bright yellow dye for nearly forty years before it was ever used as an explosive. It was used to dye cotton, silk, and even hair.)
(The image above shows hair dyed yellow with TNT, which was called 'Tol' at the time.)
But if used in torpedoes, TNT might not suffice because torpedoes need to save as much space as possible to carry more compressed air.
The first to think about improving the explosive was the Germans. In 1907, they mixed 60% TNT with 40% Hexanitrodiphenylamine (HND) and found that its explosive power was 7% stronger than 100% TNT.
