Obsolete Japanese army slang, used humorously. Not in modern use.
During the war, soldiers apparently called condoms 'totsugeki ichiban'.
Standard modern term for condom; 突撃一番 is obsolete slang.
Compound of 突撃 (charge, assault) and 一番 (number one, first), likely a humorous euphemism coined in the Japanese army. The exact origin is uncertain.