BBC,

"The Royal Navy is the oldest of the three services, and it was established by the sovereign's prerogative. For that reason, recruits have never been required to swear allegiance, but they do sign an attestation or engagement form on entry. The same applies to the Royal Marines.

For the rest of the armed forces, including the British Army and the Royal Air Force, the oath includes swearing to God "that I will be faithful and bear true allegiance to Her Majesty Queen Elizabeth the Second, her heirs and successors and that I will, as in duty bound, honestly and faithfully defend Her Majesty".


The Army and Air Force swear an oath, but Royal Navy recruits do not
Those with no religious belief can "solemnly, sincerely and truly declare and affirm."