Article 5 only applies to actions that happen in member country's home soil or military bases in North America or Europe. So if Singapore decided to blast the USS Gerald R Ford while it transisted the Straits of Malaca, Article 5 could not be invoked. It gets a bit fuzzy with the Middle East though.

Article 5: “The Parties agree that an armed attack against one or more of them in Europe or North America shall be considered an attack against them all and consequently they agree that, if such an armed attack occurs, each of them, in exercise of the right of individual or collective self-defence recognized by Article 51 of the Charter of the United Nations, will assist the Party or Parties so attacked by taking forthwith, individually and in concert with the other Parties, such action as it deems necessary, including the use of armed force, to restore and maintain