According to the RCC Catechism the Mass is essential to obtain salvation. That is the reason every effort is made on the battlefield to administer the Mass before death of a soldier. Is that correct, have I characterized the Mass properly with this? ... I’m not referring to last rites, I refer to the effort to bring a Mass to the dying man.
You actually have an incorrect understanding. I believe that you are speaking of giving Communion to the dying rather than the celebration of the Mass itself. There is a special form of Communion called Viaticum that is given to the dying. This is distinct from the Anointing of the Sick which is often called, incorrectly, the Last Rites.
Communion is one of those sacraments that are called the Sacraments of the Living. In other words, one must already be in a state of grace (i.e. saved) in order to receive it. The value of Communion is that it increases the grace of God within us, strengthening us to turn away from sin and toward the love of God. For the dying it can bring peace to the soul in a time of distress.
One is united to God, and thus saved, through Baptism. If one separates one self after Baptism through the deliberate and willful act of a serious sin then it is the sacrament of Penance, not the Mass or Communion, that is needed to have our sin forgiven and ourselves reunited to God. Communion can only be received after this.