What is the Latin equivalent of 'Faithful to the end'?

Fidelis usque ad finem is the Latin equivalent of 'Faithful to the end'. In the Word by Word translation, the adjective 'fidelis' means 'faithful'. The adverb/preposition 'usque' means 'even'. The preposition 'ad' means 'to'. The noun 'finem' means 'end'. Fidelis usque ad mortem is the Latin equivalent of 'Faithful even unto death'. In the Word by Word translation, the adjective 'fidelis' means 'faithful'. The adverb/preposition 'usque' means 'even'. The preposition 'ad' means 'to'. The noun 'mortem' means 'death'. Either way, the phrase may be used to describe the commitment of members of the Marine Corps of the United States of America. The Marine promise is one of always being faithful ['semper fidelis'] to their country, its government, and its people. That commitment is taken seriously, and doesn't end with the term of enlistment or retirement. It only ends with the end of a Marine's earthly life.