'torpedo-proofing' originates from modern English as a compound of 'torpedo' + 'proof' + suffix '-ing', where 'torpedo' names the explosive naval weapon and 'proof' (in this compound) means 'resistant to' or 'protected against'.

'torpedo' originally comes from Latin 'torpidus' (meaning 'numb, sluggish') via Italian/Spanish forms used for the electric ray (which causes numbness). In the 19th century the word was applied to an explosive naval device; 'proof' comes from Old English 'prōf' (test, trial) and developed into a suffix meaning 'resistant to' (as in 'waterproof'). The combination developed in modern English naval/technical usage as 'torpedo-proof' and then 'torpedo-proofing' for the process or result.

Initially 'torpedo' referred to an electric ray (from Latin 'torpidus' = 'numb'), and later to the naval weapon; 'proof' originally meant 'test' but evolved into a sense of 'resistant to' as a suffix. Over time the compound came to mean 'making or being resistant to torpedoes'.