In a letter addressed to the National Spiritual Assembly of the British Isles written on behalf of the Guardian he urged them to "appeal to the government for exemption from active military service in a combatant capacity, stressing the fact that in doing so they are not prompted by any selfish considerations but by the sole and supreme motive of upholding the Teachings of their Faith, which make it a moral obligation for them to desist from any act that would involve them in direct warfare with their fellow-humans or any other race or nation." [UD128]
• See other correspondence on this theme: UD122; UD134; UD259

...the Bahá'ís should continue to apply, under all circumstances, for exemption from any military duty that necessitates the taking of life. There is no justification for any change of attitude on our part at the present time.

The Universal House of Justice amplified this later statement:

There is no objection in a Bahá'í enlisting voluntarily in the armed forces of a country in order to obtain a training in some trade or profession, provided that he can do so without making himself liable to undertake combatant service. [BW17:384–5]

It is for each believer, under pain of his own conscience, to determine for himself what his actions should be, bearing in mind that the application of these principles is the spiritual obligation of every Bahá'í. It is rather for your Assembly to see that adequate instruction is provided so that the friends will let these principles be mirrored forth in their actions, and that they will be so steadfast in their love for Bahá'u'lláh that it would be unthinkable for them to willingly place themselves in a position where they must take human life. [Universal House of Justice letter to the National Spiritual Assembly of the United States ref41]