The War Prayer by Mark Twain
"It was a time of great and exalting excitement. The country was up in arms, the war was on, in every breast burned the holy fire of patriotism; the drums were beating, the bands playing, the toy pistols popping, the bunched firecrackers hissing and sputtering; on every hand and far down the receding and fading spreads of roofs and balconies a fluttering wilderness of flags flashed in the sun; daily the young volunteers marched down the wide avenue gay and fine in their new uniforms ... "
Some things never change. But the language always does. These uses of the word "gay" from a hundred years ago really stick out like a sore thumb, particularly when used in a military context.