With reference to Dr Frank Mobb's article on ecumenical councils in which he states that Vatican II declared no dogmas at all, so never exercised infallibility, allow me to make the following comment.
Of the 16 documents produced by Vatican II, only two, 'On Divine Revelation' and 'On the Church', are classified as dogmatic constitutions.
The constitution, 'On Divine Revelation', contains in its Prologue the following paragraph: 'Following in the footsteps of the Council of Trent and of Vatican I, this present Council (i.e., Vatican II) wishes to set forth authentic doctrine on divine revelation and its transmission, so that by hearing the message of salvation the whole world may believe, by believing it may hope, and by hoping it may love' (emphasis mine).
Here it is clear that the Council did not want to give a new definition of faith, but merely intended to foster a deeper insight into the mysteries of Our Lord's message of salvation.
As the full text of this constitution was submitted to the Council fathers on 18 November 1965, accepted by them with 2344 votes in favour (placet) and six votes not in favour (non placet), and subsequently promulgated on the same day by Pope Paul VI, there cannot be any doubt that the contents of this constitution - where the truth of our salvation is concerned - has to be regarded as infallible teaching of the living Magisterium of the Catholic Church who, in this case, spoke through the ecumenical council of Vatican II.
Hong Kong, China