Attack on Titan: Before the Fall Vol 13

From the Kodansha edition

The prequel to the number one bestselling Attack on Titan and winner of the Diamond Gem Award for best manga continues! UNLIKELY PARTNERS The Vertical Maneuvering Equipment, humanity's greatest weapon against the Titans, is designed at last, but there's a catch: Kuklo and the Survey Corps have only a short time to use it to successfully destroy a Titan, or the Corps will be disbanded for good. And even worse, an unlikely figure from Kuklo's past will be taking part...

Source: Penguin Random House API