English: approximate translation:

Inconceivable

Aunt

„ ... And three lieutenants were killed in the attack!”

Teenager

„ O God, O God! How can someone have the heart to kill a lieutenant!!”

This is a satire on a sheltered middle- or upper-class young woman who can't imagine why everybody doesn't admire dashing young officers in uniform the way she does. As a 19th-century young lady, the place where she most often interacts with lieutenants is at formal social events like balls, where they're attired in their fancy-dress uniforms, and where the young ladies attending these events enjoy flirting and dancing with them. The particular attraction of lieutenants is that those with a lower military rank would be non-officers, and so belong to a lower social class (and thus would be completely ineligible as potential suitors), while many of those with a higher military rank would already be married. So when she wonders why anybody would be so hard-hearted as to kill a lieutenant, it's not out of a vague generalized non-specific benevolence, but rather because she vividly pictures them as she has encountered them, available eligible bachelors in their shiny fancy-dress uniforms, elegantly flirting with and flattering young ladies