KYIV, Ukraine — Just over a year ago, Yulia Bondarenko’s days were full of lesson plans, grading and her students’ seventh grade hormones.

When Russian missiles shattered that routine and Russian troops threatened her home in Kyiv, Ukraine’s capital, Bondarenko, 30, volunteered to fight back, despite her lack of experience, the grave risk to her life and Ukraine’s apparently impossible odds.

“I never held a rifle in my hands and never even saw one up close,” Bondarenko said. “In the first two weeks, I felt like I was in a fog. It was just a constant nightmare.”

For weeks, she had followed the ominous news of Russian troops massing on Ukraine’s border and decided Feb. 23 to enlist as a reservist. The next day, the largest land war in Europe since World War II began.

As explosions shook Kyiv, Bondarenko took the subway to report for duty, uncertain that the recruiting office would take her without finished paperwork or a fitness exam.

But in the chaotic swirl of volunteers, officers asked no questions. They handed her a rifle and 120 bullets, and assigned her to a unit expecting to fight in urban combat if the Russian army broke into the capital. She was only one recruit in a huge influx of volunteers who swelled the size of Ukrainian forces — from about 260,000 soldiers to about 1 million today — and whose lives were transformed by the war.