Sengoku Jieitai 1549 summary:

A military test accidentally sends a modern-day army back in time to feudal Japan. When their actions in the past begin to have an effect on the present, another unit is dispatched to retrieve them. But the commander of the lost unit has other plans. He intends to use his advanced technology to conquer Japan and change his country's destiny.-- {Summary by Mangaupdates.com}