Kyiv, Ukraine CNN  —  Editor’s Note: This report contains details of death and injury that some may find distressing. More than 20 Americans are missing in action on the front lines in Ukraine, with a spike in casualties over the past six months as foreigners fill urgent gaps in the country’s embattled defenses, according to a CNN investigation. The bodies of at least five American volunteers who signed up to the Ukrainian military could not be retrieved from the battlefield after being killed