Art 21. The Parties to the conflict may appeal to the charity of commanders of neutral merchant vessels, yachts or other craft, to take on board and care for wounded, sick or shipwrecked persons, and to collect the dead. Vessels of any kind responding to this appeal, and those having of their own accord collected wounded, sick or shipwrecked persons, shall enjoy special protection and facilities to carry out such assistance. They may, in no case, be captured on account of any such transport; but, in the absence of any promise to the contrary, they shall remain liable to capture for any violations of neutrality they may have committed.