When merchant ships come under naval rules

Do non-RFA merchant ships also become part of the Royal Navy in wartime?

Only in some cases: ships taken under naval control can be subject to naval rules, while ordinary convoy merchants remain merchant ships.

The answer distinguishes ships formally taken under naval control from ordinary merchants sailing in convoy. Wartime obligations therefore depend on the terms under which the ship has been taken up from trade. A vessel merely sailing in convoy does not automatically become a Royal Navy ship. The distinction matters because legal authority over the crew follows the contract and control arrangement, not simply the ship's presence in a naval operation.