Catechism of the Catholic Church §2310 — excerpt
Public authorities, in this case, have the right and duty to impose on citizens the obligations necessary for national defense. Those who are sworn to serve their country in the armed forces are servants of the security and freedom of nations.
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.
Also cites: GS 79 # 5