Objection 1. It seems that fortitude is not properly about dangers of death in battle. For martyrs above all are commended for their fortitude. But martyrs are not commended in connection with battle. Therefore fortitude is not properly about dangers of death in battle.
Objection 2. Further, Ambrose says (De Offic. i) that "fortitude is applicable both to warlike and to civil matters": and Tully (De Offic. i), under the heading, "That it pertains to fortitude to excel in battle rather than in civil life," says: "Although not a few think that the business of war is of greater importance than the affairs of civil life, this opinion must be qualified: and if we wish to judge the matter truly, there are many things in civil life that are more important and more glorious than those connected with war." Now greater fortitude is about greater things. Therefore fortitude is not properly concerned with death in battle.
Objection 3. Further, war is directed to the preservation of a country's temporal peace: for Augustine says (De Civ. Dei xix) that "wars are waged in order to insure peace." Now it does not seem that one ought to expose oneself to the danger of death for the temporal peace of one's country, since this same peace is the occasion of much license in morals. Therefore it seems that the virtue of fortitude is not about the danger of death in battle.
On the contrary, The Philosopher says (Ethic. iii) that fortitude is chiefly about death in battle.
I answer that, As stated above (Article 4), fortitude strengthens a man's mind against the greatest danger, which is that of death. Now fortitude is a virtue; and it is essential to virtue ever to tend to good; wherefore it is in order to pursue some good that man does not fly from the danger of death. But the dangers of death arising out of sickness, storms at sea, attacks from robbers, and the like, do not seem to come on a man through his pursuing some good. on the other hand, the dangers of death which occur in battle come to man directly on account of some good, because, to wit, he is defending the common good by a just fight. Now a just fight is of two kinds. First, there is the general combat, for instance, of those who fight in battle; secondly, there is the private combat, as when a judge or even private individual does not refrain from giving a just judgment through fear of the impending sword, or any other danger though it threaten death. Hence it belongs to fortitude to strengthen the mind against dangers of death, not only such as arise in a general battle, but also such as occur in singular combat, which may be called by the general name of battle. Accordingly it must be granted that fortitude is properly about dangers of death occurring in battle.
Moreover, a brave man behaves well in face of danger of any other kind of death; especially since man may be in danger of any kind of death on account of virtue: thus may a man not fail to attend on a sick friend through fear of deadly infection, or not refuse to undertake a journey with some godly object in view through fear of shipwreck or robbers.
Reply to Objection 1. Martyrs face the fight that is waged against their own person, and this for the sake of the sovereign good which is God; wherefore their fortitude is praised above all. Nor is it outside the genus of fortitude that regards warlike actions, for which reason they are said to have been valiant in battle. [Office of Martyrs, ex. Heb. xi. 34.]
Reply to Objection 2. Personal and civil business is differentiated from the business of war that regards general wars. However, personal and civil affairs admit of dangers of death arising out of certain conflicts which are private wars, and so with regard to these also there may be fortitude properly so called.
Reply to Objection 3. The peace of the state is good in itself, nor does it become evil because certain persons make evil use of it. For there are many others who make good use of it; and many evils prevented by it, such as murders and sacrileges, are much greater than those which are occasioned by it, and which belong chiefly to the sins of the flesh.
Source: Summa Theologica (New Advent)