Attendance at a Protestant service does not fulfill the Sunday obligation. The first precept of the Church requires the faithful to “sanctify the day commemorating the Resurrection of the Lord as well as the principal liturgical feasts…. by participating in the Eucharistic celebration, in which the Christian community is gathered.” (CCC 2042)
However, if participation in the celebration of the Eucharist is impossible, you have no obligation to attend Mass. In this situation, the Church recommends that “the faithful take part in the Liturgy of the Word if it is celebrated in the parish church or in another sacred place according to the prescriptions of the diocesan bishop, or engage in prayer for an appropriate amount of time personally or in a family or, as occasion offers, in groups of families." CCC 2183
Pope John Paul II in his encyclical *Ecclesia de Eucharista * states:
“The Catholic faithful, therefore, while respecting the religious convictions of these separated brethren, must refrain from receiving the communion distributed in their celebrations, so as not to condone an ambiguity about the nature of the Eucharist and, consequently, to fail in their duty to bear clear witness to the truth. This would result in slowing the progress being made towards full visible unity.
Similarly, it is unthinkable to substitute for Sunday Mass ecumenical celebrations of the word or services of common prayer with Christians from the aforementioned Ecclesial Communities, or even participation in their own liturgical services. Such celebrations and services, however praiseworthy in certain situations, prepare for the goal of full communion, including Eucharistic communion, but they cannot replace it.” (30)
Source: Ecclesia de Eucharista
God bless you, and thank you for your service to our country. You are in our prayers.